[compiler] More claude config

Uses a simple algorithm for detecting writes of refs during render, since the ref _read_ during render is now handled as part of ValidateNoImpureValuesInRender.

compiler/.claude/settings.local.json

@@ -1,7 +1,18 @@
 {
   "permissions": {
     "allow": [
-      "Bash(node scripts/enable-feature-flag.js:*)"
+      "Bash(node scripts/enable-feature-flag.js:*)",
+      "Bash(yarn snap:*)",
+      "Bash(for test in \"error.invalid-access-ref-during-render\" \"error.invalid-ref-in-callback-invoked-during-render\" \"error.invalid-impure-functions-in-render-via-render-helper\")",
+      "Bash(do)",
+      "Bash(echo:*)",
+      "Bash(done)",
+      "Bash(cat:*)",
+      "Bash(sl revert:*)",
+      "Bash(yarn workspace snap run build:*)",
+      "Bash(yarn tsc:*)",
+      "Bash(yarn snap:build)",
+      "Bash(timeout 30 yarn snap:*)"
     ],
     "deny": [],
     "ask": []

compiler/CLAUDE.md

@@ -0,0 +1,245 @@
+# React Compiler Knowledge Base
+
+This document contains knowledge about the React Compiler gathered during development sessions. It serves as a reference for understanding the codebase architecture and key concepts.
+
+## Project Structure
+
+- `packages/babel-plugin-react-compiler/` - Main compiler package
+  - `src/HIR/` - High-level Intermediate Representation types and utilities
+  - `src/Inference/` - Effect inference passes (aliasing, mutation, etc.)
+  - `src/Validation/` - Validation passes that check for errors
+  - `src/Entrypoint/Pipeline.ts` - Main compilation pipeline with pass ordering
+  - `src/__tests__/fixtures/compiler/` - Test fixtures
+    - `error.*.js` - Fixtures that should produce compilation errors
+    - `*.expect.md` - Expected output for each fixture
+
+## Running Tests
+
+```bash
+# Run all tests
+yarn snap
+
+# Run specific test by pattern
+yarn snap -p <pattern>
+
+# Update fixture outputs
+yarn snap -u
+```
+
+## Version Control
+
+This repository uses Sapling (`sl`) for version control. Unlike git, Sapling does not require explicitly adding files to the staging area.
+
+```bash
+# Check status
+sl status
+
+# Commit all changes
+sl commit -m "Your commit message"
+
+# Commit with multi-line message using heredoc
+sl commit -m "$(cat <<'EOF'
+Summary line
+
+Detailed description here
+EOF
+)"
+```
+
+## Key Concepts
+
+### HIR (High-level Intermediate Representation)
+
+The compiler converts source code to HIR for analysis. Key types in `src/HIR/HIR.ts`:
+
+- **HIRFunction** - A function being compiled
+  - `body.blocks` - Map of BasicBlocks
+  - `context` - Captured variables from outer scope
+  - `params` - Function parameters
+  - `returns` - The function's return place
+  - `aliasingEffects` - Effects that describe the function's behavior when called
+
+- **Instruction** - A single operation
+  - `lvalue` - The place being assigned to
+  - `value` - The instruction kind (CallExpression, FunctionExpression, LoadLocal, etc.)
+  - `effects` - Array of AliasingEffects for this instruction
+
+- **Terminal** - Block terminators (return, branch, etc.)
+  - `effects` - Array of AliasingEffects
+
+- **Place** - A reference to a value
+  - `identifier.id` - Unique IdentifierId
+
+- **Phi nodes** - Join points for values from different control flow paths
+  - Located at `block.phis`
+  - `phi.place` - The result place
+  - `phi.operands` - Map of predecessor block to source place
+
+### AliasingEffects System
+
+Effects describe data flow and operations. Defined in `src/Inference/AliasingEffects.ts`:
+
+**Data Flow Effects:**
+- `Impure` - Marks a place as containing an impure value (e.g., Date.now() result, ref.current)
+- `Capture a -> b` - Value from `a` is captured into `b` (mutable capture)
+- `Alias a -> b` - `b` aliases `a`
+- `ImmutableCapture a -> b` - Immutable capture (like Capture but read-only)
+- `Assign a -> b` - Direct assignment
+- `MaybeAlias a -> b` - Possible aliasing
+- `CreateFrom a -> b` - Created from source
+
+**Mutation Effects:**
+- `Mutate value` - Value is mutated
+- `MutateTransitive value` - Value and transitive captures are mutated
+- `MutateConditionally value` - May mutate
+- `MutateTransitiveConditionally value` - May mutate transitively
+
+**Other Effects:**
+- `Render place` - Place is used in render context (JSX props, component return)
+- `Freeze place` - Place is frozen (made immutable)
+- `Create place` - New value created
+- `CreateFunction` - Function expression created, includes `captures` array
+- `Apply` - Function application with receiver, function, args, and result
+
+### Hook Aliasing Signatures
+
+Located in `src/HIR/Globals.ts`, hooks can define custom aliasing signatures to control how data flows through them.
+
+**Structure:**
+```typescript
+aliasing: {
+  receiver: '@receiver',    // The hook function itself
+  params: ['@param0'],      // Named positional parameters
+  rest: '@rest',            // Rest parameters (or null)
+  returns: '@returns',      // Return value
+  temporaries: [],          // Temporary values during execution
+  effects: [                // Array of effects to apply when hook is called
+    {kind: 'Freeze', value: '@param0', reason: ValueReason.HookCaptured},
+    {kind: 'Assign', from: '@param0', into: '@returns'},
+  ],
+}
+```
+
+**Common patterns:**
+
+1. **RenderHookAliasing** (useState, useContext, useMemo, useCallback):
+   - Freezes arguments (`Freeze @rest`)
+   - Marks arguments as render-time (`Render @rest`)
+   - Creates frozen return value
+   - Aliases arguments to return
+
+2. **EffectHookAliasing** (useEffect, useLayoutEffect, useInsertionEffect):
+   - Freezes function and deps
+   - Creates internal effect object
+   - Captures function and deps into effect
+   - Returns undefined
+
+3. **Event handler hooks** (useEffectEvent):
+   - Freezes callback (`Freeze @fn`)
+   - Aliases input to return (`Assign @fn -> @returns`)
+   - NO Render effect (callback not called during render)
+
+**Example: useEffectEvent**
+```typescript
+const UseEffectEventHook = addHook(
+  DEFAULT_SHAPES,
+  {
+    positionalParams: [Effect.Freeze],  // Takes one positional param
+    restParam: null,
+    returnType: {kind: 'Function', ...},
+    calleeEffect: Effect.Read,
+    hookKind: 'useEffectEvent',
+    returnValueKind: ValueKind.Frozen,
+    aliasing: {
+      receiver: '@receiver',
+      params: ['@fn'],              // Name for the callback parameter
+      rest: null,
+      returns: '@returns',
+      temporaries: [],
+      effects: [
+        {kind: 'Freeze', value: '@fn', reason: ValueReason.HookCaptured},
+        {kind: 'Assign', from: '@fn', into: '@returns'},
+        // Note: NO Render effect - callback is not called during render
+      ],
+    },
+  },
+  BuiltInUseEffectEventId,
+);
+
+// Add as both names for compatibility
+['useEffectEvent', UseEffectEventHook],
+['experimental_useEffectEvent', UseEffectEventHook],
+```
+
+**Key insight:** If a hook is missing an `aliasing` config, it falls back to `DefaultNonmutatingHook` which includes a `Render` effect on all arguments. This can cause false positives for hooks like `useEffectEvent` whose callbacks are not called during render.
+
+### Effect Inference Pipeline
+
+Effects are populated by `InferMutationAliasingEffects` (runs before validation):
+
+1. For `Date.now()`, `Math.random()` etc. - adds `Impure` effect (controlled by `validateNoImpureFunctionsInRender` config)
+2. For `ref.current` access - adds `Impure` effect (controlled by `validateRefAccessDuringRender` config)
+3. For return terminals - adds `Alias` from return value to `fn.returns`
+4. For component/JSX returns - adds `Render` effect
+5. For function expressions - adds `CreateFunction` effect with captures
+
+### Validation: validateNoImpureValuesInRender
+
+Located at `src/Validation/ValidateNoImpureValuesInRender.ts`
+
+**Purpose:** Detect when impure values (refs, Date.now results, etc.) flow into render context.
+
+**Algorithm:**
+1. Track impure values in a Map<IdentifierId, ImpureEffect>
+2. Track functions with impure returns separately (they're not impure values themselves)
+3. Fixed-point iteration over all blocks:
+   - Process phi nodes (any impure operand makes result impure)
+   - Process instruction effects
+   - Process terminal effects
+   - Backwards propagation for mutated LoadLocal values
+4. Validate: check all Render effects against impure values
+
+**Key patterns:**
+- `Impure` effect marks the target as impure
+- `Capture/Alias/etc` propagates impurity from source to target
+- `Apply` propagates impurity from args/receiver to result
+- `CreateFunction` propagates impurity from captured values (but NOT from body effects)
+- If a value has both `Render` and `Capture` in same instruction, only error on Render (don't cascade)
+
+**Tracking functions with impure returns:**
+- Separate from the `impure` map (function values aren't impure, just their returns)
+- Populated when analyzing FunctionExpression bodies
+- Used when:
+  1. Calling the function - mark call result as impure
+  2. Capturing the function - mark target as impure (for object.foo = impureFunc cases)
+
+**Backwards propagation:**
+- When `$x = LoadLocal y` and `$x` is mutated with impure content, mark `y` as impure
+- This handles: `const arr = []; arr.push(impure); render(arr)`
+
+## Known Issues / Edge Cases
+
+### Function Outlining
+After `OutlineFunctions` pass, inner functions are replaced with `LoadGlobal(_temp)`. The validation runs BEFORE outlining, so it sees the original FunctionExpression. But be aware that test output shows post-outlining HIR.
+
+### SSA and LoadLocal
+In SSA form, each `LoadLocal` creates a new identifier. When a loaded value is mutated:
+- `$x = LoadLocal y`
+- `mutate($x, impure)`
+- `$z = LoadLocal y` (different from $x!)
+- `render($z)`
+
+The impurity in $x must propagate back to y, then forward to $z. This requires backwards propagation in the fixed-point loop.
+
+## Configuration Flags
+
+In `Environment.ts` / test directives:
+- `validateNoImpureFunctionsInRender` - Enable impure function validation (Date.now, Math.random, etc.)
+- `validateRefAccessDuringRender` - Enable ref access validation
+
+## Debugging Tips
+
+1. Run `yarn snap -p <fixture>` to see full HIR output with effects
+2. Look for `@aliasingEffects=` on FunctionExpressions
+3. Look for `Impure`, `Render`, `Capture` effects on instructions
+4. Check the pass ordering in Pipeline.ts to understand when effects are populated vs validated

compiler/packages/babel-plugin-react-compiler/src/HIR/Globals.ts

@@ -822,6 +822,22 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
       calleeEffect: Effect.Read,
       hookKind: 'useRef',
       returnValueKind: ValueKind.Mutable,
+      aliasing: {
+        receiver: '@receiver',
+        params: [],
+        rest: '@rest',
+        returns: '@return',
+        temporaries: [],
+        effects: [
+          {
+            kind: 'Create',
+            into: '@return',
+            value: ValueKind.Mutable,
+            reason: ValueReason.KnownReturnSignature,
+          },
+          {kind: 'Capture', from: '@rest', into: '@return'},
+        ],
+      },
     }),
   ],
   [
@@ -852,7 +868,12 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
     addHook(DEFAULT_SHAPES, {
       positionalParams: [],
       restParam: Effect.Freeze,
-      returnType: {kind: 'Poly'},
+      returnType: {
+        kind: 'Function',
+        isConstructor: false,
+        return: {kind: 'Poly'},
+        shapeId: null,
+      },
       calleeEffect: Effect.Read,
       hookKind: 'useCallback',
       returnValueKind: ValueKind.Frozen,

compiler/packages/babel-plugin-react-compiler/src/HIR/PrintHIR.ts

@@ -983,15 +983,15 @@ export function printAliasingEffect(effect: AliasingEffect): string {
           return `...${printPlaceForAliasEffect(arg.place)}`;
         })
         .join(', ');
-      let signature = '';
-      if (effect.signature != null) {
-        if (effect.signature.aliasing != null) {
-          signature = printAliasingSignature(effect.signature.aliasing);
-        } else {
-          signature = JSON.stringify(effect.signature, null, 2);
-        }
-      }
-      return `Apply ${printPlaceForAliasEffect(effect.into)} = ${receiverCallee}(${args})${signature != '' ? '\n     ' : ''}${signature}`;
+      // let signature = '';
+      // if (effect.signature != null) {
+      //   if (effect.signature.aliasing != null) {
+      //     signature = printAliasingSignature(effect.signature.aliasing);
+      //   } else {
+      //     signature = JSON.stringify(effect.signature, null, 2);
+      //   }
+      // }
+      return `Apply ${printPlaceForAliasEffect(effect.into)} = ${receiverCallee}(${args})`;
     }
     case 'Freeze': {
       return `Freeze ${printPlaceForAliasEffect(effect.value)} ${effect.reason}`;

compiler/packages/babel-plugin-react-compiler/src/Inference/InferMutationAliasingEffects.ts

@@ -1094,6 +1094,8 @@ function applyEffect(
       break;
     }
     case 'Apply': {
+      effects.push(effect);
+
       const functionValues = state.values(effect.function);
       if (
         functionValues.length === 1 &&
@@ -2201,14 +2203,8 @@ function computeSignatureForInstruction(
           if (isUseRefType(place.identifier)) {
             continue;
           }
-          if (place.identifier.type.kind === 'Function') {
-            if (isJsxOrJsxUnionType(place.identifier.type.return)) {
-              effects.push({
-                kind: 'Render',
-                place,
-              });
-            }
-          } else {
+          if (place.identifier.type.kind !== 'Function') {
+            // Functions are checked independently
             effects.push({
               kind: 'Render',
               place,

compiler/packages/babel-plugin-react-compiler/src/Inference/InferMutationAliasingRanges.ts

@@ -20,6 +20,7 @@ import {
   Place,
   isPrimitiveType,
   isUseRefType,
+  isJsxOrJsxUnionType,
 } from '../HIR/HIR';
 import {
   eachInstructionLValue,
@@ -396,17 +397,7 @@ export function inferMutationAliasingRanges(
             break;
           }
           case 'Apply': {
-            CompilerError.invariant(false, {
-              reason: `[AnalyzeFunctions] Expected Apply effects to be replaced with more precise effects`,
-              description: null,
-              details: [
-                {
-                  kind: 'error',
-                  loc: effect.function.loc,
-                  message: null,
-                },
-              ],
-            });
+            break;
           }
           case 'MutateTransitive':
           case 'MutateConditionally':
@@ -588,7 +579,12 @@ export function inferMutationAliasingRanges(
     }
   }
 
-  if (errors.hasAnyErrors() && !isFunctionExpression) {
+  if (
+    errors.hasAnyErrors() &&
+    (fn.fnType === 'Component' ||
+      isJsxOrJsxUnionType(fn.returns.identifier.type) ||
+      !isFunctionExpression)
+  ) {
     return Err(errors);
   }
   return Ok(functionEffects);

compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoImpureValuesInRender.ts

@@ -5,7 +5,6 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import prettyFormat from 'pretty-format';
 import {CompilerDiagnostic, CompilerError, Effect} from '..';
 import {
   areEqualSourceLocations,
@@ -13,35 +12,30 @@ import {
   IdentifierId,
   InstructionId,
   isJsxType,
-  isRefValueType,
   isUseRefType,
 } from '../HIR';
-import {
-  eachInstructionLValue,
-  eachInstructionValueOperand,
-} from '../HIR/visitors';
-import {AliasingEffect} from '../Inference/AliasingEffects';
+import {AliasingEffect, hashEffect} from '../Inference/AliasingEffects';
 import {createControlDominators} from '../Inference/ControlDominators';
 import {isMutable} from '../ReactiveScopes/InferReactiveScopeVariables';
 import {Err, Ok, Result} from '../Utils/Result';
-import {
-  assertExhaustive,
-  getOrInsertWith,
-  Set_filter,
-  Set_subtract,
-} from '../Utils/utils';
-import {printInstruction} from '../HIR/PrintHIR';
+import {getOrInsertWith} from '../Utils/utils';
+import {printFunction} from '../HIR/PrintHIR';
 
 type ImpureEffect = Extract<AliasingEffect, {kind: 'Impure'}>;
 type RenderEffect = Extract<AliasingEffect, {kind: 'Render'}>;
 type FunctionCache = Map<HIRFunction, Map<string, ImpuritySignature>>;
-type ImpuritySignature = {effects: Array<ImpureEffect>; error: CompilerError};
+type ImpuritySignature = {
+  effects: Map<IdentifierId, ImpureEffect>;
+  error: CompilerError;
+  returns: IdentifierId;
+};
 
 export function validateNoImpureValuesInRender(
   fn: HIRFunction,
 ): Result<void, CompilerError> {
   const impure = new Map<IdentifierId, ImpureEffect>();
-  const result = inferImpureValues(fn, impure, new Map());
+  const impureFunctions = new Map<IdentifierId, ImpuritySignature>();
+  const result = inferImpureValues(fn, impure, impureFunctions, new Map());
 
   if (result.error.hasAnyErrors()) {
     return Err(result.error);
@@ -52,15 +46,23 @@ export function validateNoImpureValuesInRender(
 function inferFunctionExpressionMemo(
   fn: HIRFunction,
   impure: Map<IdentifierId, ImpureEffect>,
+  impureFunctions: Map<IdentifierId, ImpuritySignature>,
   cache: FunctionCache,
 ): ImpuritySignature {
   const key = fn.context
-    .map(place => `${place.identifier.id}:${impure.has(place.identifier.id)}`)
+    .map(
+      place =>
+        `${place.identifier.id}:${impure.has(place.identifier.id)}:${Array.from(
+          impureFunctions.get(place.identifier.id)?.effects ?? new Map(),
+        )
+          .map(([id, effect]) => `${id}=>${effect.into.identifier.id}`)
+          .join(',')}`,
+    )
     .join(',');
   return getOrInsertWith(
     getOrInsertWith(cache, fn, () => new Map()),
     key,
-    () => inferImpureValues(fn, impure, cache),
+    () => inferImpureValues(fn, impure, impureFunctions, cache),
   );
 }
 
@@ -68,6 +70,7 @@ function processEffects(
   id: InstructionId,
   effects: Array<AliasingEffect>,
   impure: Map<IdentifierId, ImpureEffect>,
+  impureFunctions: Map<IdentifierId, ImpuritySignature>,
   cache: FunctionCache,
 ): boolean {
   let hasChanges = false;
@@ -92,6 +95,9 @@ function processEffects(
           !isUseRefType(effect.into.identifier) &&
           !isJsxType(effect.into.identifier.type)
         ) {
+          // console.log(
+          //   `${effect.kind} $${effect.into.identifier.id} <= $${effect.from.identifier.id} ($${sourceEffect.into.identifier.id} forward)`,
+          // );
           impure.set(effect.into.identifier.id, sourceEffect);
           hasChanges = true;
         }
@@ -105,14 +111,42 @@ function processEffects(
         ) {
           const destinationEffect = impure.get(effect.into.identifier.id);
           if (destinationEffect != null) {
+            // console.log(
+            //   `${effect.kind} $${effect.into.identifier.id} => $${effect.from.identifier.id} ($${destinationEffect.into.identifier.id} backward)`,
+            // );
             impure.set(effect.from.identifier.id, destinationEffect);
             hasChanges = true;
           }
         }
+        if (
+          (effect.kind === 'Alias' ||
+            effect.kind === 'Assign' ||
+            effect.kind === 'ImmutableCapture') &&
+          !rendered.has(effect.into.identifier.id) &&
+          !isJsxType(effect.into.identifier.type)
+        ) {
+          const functionEffect = impureFunctions.get(effect.from.identifier.id);
+          if (
+            functionEffect != null &&
+            !impureFunctions.has(effect.into.identifier.id)
+            // ||
+            //   !areEqualFunctionSignatures(
+            //     impureFunctions.get(effect.into.identifier.id)!.effects,
+            //     functionEffect.effects,
+            //   )
+          ) {
+            // console.log(
+            //   `${effect.kind} $${effect.into.identifier.id} <= $${effect.from.identifier.id} (function)`,
+            // );
+            impureFunctions.set(effect.into.identifier.id, functionEffect);
+            hasChanges = true;
+          }
+        }
         break;
       }
       case 'Impure': {
         if (!impure.has(effect.into.identifier.id)) {
+          // console.log(`Impure $${effect.into.identifier.id}`);
           impure.set(effect.into.identifier.id, effect);
           hasChanges = true;
         }
@@ -125,26 +159,45 @@ function processEffects(
         const result = inferFunctionExpressionMemo(
           effect.function.loweredFunc.func,
           impure,
+          impureFunctions,
           cache,
         );
         if (result.error.hasAnyErrors()) {
           break;
         }
-        const impureEffect: ImpureEffect | null =
-          result.effects.find(
-            (functionEffect: AliasingEffect): functionEffect is ImpureEffect =>
-              functionEffect.kind === 'Impure' &&
-              functionEffect.into.identifier.id ===
-                effect.function.loweredFunc.func.returns.identifier.id,
-          ) ?? null;
-        if (impureEffect != null) {
-          impure.set(effect.into.identifier.id, impureEffect);
+        const previousResult = impureFunctions.get(effect.into.identifier.id);
+        if (
+          previousResult == null ||
+          !areEqualFunctionSignatures(result.effects, previousResult.effects)
+        ) {
+          // console.log(`Function $${effect.into.identifier.id}`);
+          impureFunctions.set(effect.into.identifier.id, result);
           hasChanges = true;
         }
         break;
       }
+      case 'Apply': {
+        const functionSignature = impureFunctions.get(
+          effect.function.identifier.id,
+        );
+        if (functionSignature != null) {
+          for (const [id, functionEffect] of functionSignature.effects) {
+            if (!impure.has(id)) {
+              impure.set(id, functionEffect);
+              hasChanges = true;
+            }
+            if (
+              id === functionSignature.returns &&
+              !impure.has(effect.into.identifier.id)
+            ) {
+              impure.set(effect.into.identifier.id, functionEffect);
+              hasChanges = true;
+            }
+          }
+        }
+        break;
+      }
       case 'MaybeAlias':
-      case 'Apply':
       case 'Create':
       case 'Freeze':
       case 'Mutate':
@@ -163,6 +216,7 @@ function processEffects(
 function inferImpureValues(
   fn: HIRFunction,
   impure: Map<IdentifierId, ImpureEffect>,
+  impureFunctions: Map<IdentifierId, ImpuritySignature>,
   cache: FunctionCache,
 ): ImpuritySignature {
   const getBlockControl = createControlDominators(fn, place => {
@@ -170,9 +224,14 @@ function inferImpureValues(
   });
 
   let hasChanges = false;
+  let iterations = 0;
   do {
     hasChanges = false;
 
+    if (iterations++ > 100) {
+      throw new Error('too many iterations');
+    }
+
     for (const block of fn.body.blocks.values()) {
       const controlPlace = getBlockControl(block.id);
       const controlImpureEffect =
@@ -212,8 +271,13 @@ function inferImpureValues(
       for (const instr of block.instructions) {
         const _impure = new Set(impure.keys());
         hasChanges =
-          processEffects(instr.id, instr.effects ?? [], impure, cache) ||
-          hasChanges;
+          processEffects(
+            instr.id,
+            instr.effects ?? [],
+            impure,
+            impureFunctions,
+            cache,
+          ) || hasChanges;
       }
       if (block.terminal.kind === 'return' && block.terminal.effects != null) {
         hasChanges =
@@ -221,6 +285,7 @@ function inferImpureValues(
             block.terminal.id,
             block.terminal.effects,
             impure,
+            impureFunctions,
             cache,
           ) || hasChanges;
       }
@@ -232,10 +297,19 @@ function inferImpureValues(
     name: 'ValidateNoImpureValuesInRender',
     value: JSON.stringify(Array.from(impure.keys()).sort(), null, 2),
   });
+  fn.env.logger?.debugLogIRs?.({
+    kind: 'debug',
+    name: 'ValidateNoImpureValuesInRender (function)',
+    value: JSON.stringify(Array.from(impureFunctions.keys()).sort(), null, 2),
+  });
 
   const error = new CompilerError();
   function validateRenderEffect(effect: RenderEffect): void {
-    const impureEffect = impure.get(effect.place.identifier.id);
+    let impureEffect = impure.get(effect.place.identifier.id);
+    if (impureEffect == null) {
+      const functionSignature = impureFunctions.get(effect.place.identifier.id);
+      impureEffect = functionSignature?.effects.get(functionSignature.returns);
+    }
     if (impureEffect == null) {
       return;
     }
@@ -267,6 +341,7 @@ function inferImpureValues(
         const result = inferFunctionExpressionMemo(
           value.loweredFunc.func,
           impure,
+          impureFunctions,
           cache,
         );
         if (result.error.hasAnyErrors()) {
@@ -287,21 +362,26 @@ function inferImpureValues(
       }
     }
   }
-  const impureEffects: Array<ImpureEffect> = [];
+  const impureEffects: Map<IdentifierId, ImpureEffect> = new Map();
   for (const param of [...fn.context, ...fn.params, fn.returns]) {
     const place = param.kind === 'Identifier' ? param : param.place;
     const impureEffect = impure.get(place.identifier.id);
     if (impureEffect != null) {
-      impureEffects.push({
-        kind: 'Impure',
-        into: impureEffect.into,
-        category: impureEffect.category,
-        reason: impureEffect.reason,
-        description: impureEffect.description,
-        sourceMessage: impureEffect.sourceMessage,
-        usageMessage: impureEffect.usageMessage,
-      });
+      impureEffects.set(place.identifier.id, impureEffect);
     }
   }
-  return {effects: impureEffects, error};
+  return {effects: impureEffects, error, returns: fn.returns.identifier.id};
+}
+
+function areEqualFunctionSignatures(
+  sig1: Map<IdentifierId, ImpureEffect>,
+  sig2: Map<IdentifierId, ImpureEffect>,
+): boolean {
+  return (
+    sig1.size === sig2.size &&
+    Array.from(sig1).every(
+      ([id, effect]) =>
+        sig2.has(id) && hashEffect(effect) === hashEffect(sig2.get(id)!),
+    )
+  );
 }

compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoRefAccessInRender.md

@@ -0,0 +1,137 @@
+# ValidateNoRefAccessInRender
+
+This document summarizes the design and key learnings for the ref mutation validation pass.
+
+## Purpose
+
+Validates that a function does not mutate a ref value during render. This ensures React components follow the rules of React by not writing to `ref.current` during the render phase.
+
+## Key Concepts
+
+### Ref vs RefValue
+
+- **Ref**: The ref object itself (e.g., `useRef()` return value). Has type `React.RefObject<T>`.
+- **RefValue**: The `.current` property of a ref. This is the mutable value that should not be accessed during render.
+
+The validation tracks both using a `RefInfo` type with a `refId` that correlates refs with their `.current` values.
+
+### What Constitutes a Mutation
+
+A mutation is any `PropertyStore` or `ComputedStore` instruction where:
+1. The target object is a known ref (tracked in the `refs` map)
+2. OR the target object has a ref type (`isUseRefType`)
+
+### Allowed Patterns
+
+1. **Event handlers and effect callbacks**: Functions that are not called at the top level during render can mutate refs freely.
+
+2. **Null-guard initialization**: The pattern `if (ref.current == null) { ref.current = value; }` is allowed because it's a common lazy initialization pattern that only runs once.
+
+## Algorithm: Single Forward Data-Flow Pass
+
+The validation uses a single forward pass over all blocks:
+
+### Phase 1: Track Refs
+- Initialize refs from function params and context (captured variables)
+- Process phi nodes to propagate ref info through control flow joins
+- Track refs through LoadLocal, StoreLocal, PropertyLoad operations
+
+### Phase 2: Detect Null Guards
+- Track nullable values (null literals, undefined)
+- Track binary comparisons of `ref.current` to null (`==`, `===`, `!=`, `!==`)
+- Mark blocks as "safe" for specific refs when inside null-guard branches
+- Propagate safety through control flow until fallthrough
+
+### Phase 3: Validate Mutations
+- For PropertyStore/ComputedStore on refs:
+  - If inside a null-guard for this ref: allow (but track for duplicate detection)
+  - If at top level: error immediately
+  - If in nested function: track for later (error if function is called)
+
+### Phase 4: Track Ref-Mutating Functions
+- When a FunctionExpression mutates a ref, track it in `refMutatingFunctions`
+- When such a function is called at top level, report the error at the mutation site
+
+## Key Data Structures
+
+```typescript
+// Correlates refs with their .current values
+type RefInfo = {
+  kind: 'Ref' | 'RefValue';
+  refId: number;
+};
+
+// Tracks null-guard conditions
+type GuardInfo = {
+  refId: number;
+  isEquality: boolean; // true for ==, ===; false for !=, !==
+};
+
+// Information about a mutation (for error reporting)
+type MutationInfo = {
+  loc: SourceLocation;
+  isCurrentProperty: boolean;
+};
+```
+
+## Error Reporting
+
+### Error Location
+
+Errors highlight the **entire instruction** (e.g., `ref.current = value`), not just the ref identifier. This is achieved by using `instr.loc` instead of `value.object.loc`.
+
+### Duplicate Initialization
+
+When a ref is initialized more than once inside a null-guard:
+1. Primary error: Points to the second initialization
+2. Secondary error: Points to the first initialization with "Ref was first initialized here"
+
+### Transitive Mutations
+
+When a function that mutates refs is called during render:
+- The error points to the mutation site inside the function
+- Not the call site (the call site is what triggers the check)
+
+## Edge Cases and Patterns
+
+### Unary NOT on Guards
+
+The `!` operator inverts guard polarity:
+```javascript
+if (!ref.current) { ... }  // Same as: if (ref.current == null)
+```
+
+### Nested Functions
+
+Functions defined during render but not called are allowed to mutate refs:
+```javascript
+// OK - onClick is not called during render
+const onClick = () => { ref.current = value; };
+return <button onClick={onClick} />;
+```
+
+### Props with Ref Type
+
+Refs can come from props. The validation handles `props.ref` by checking type information.
+
+## Limitations / Known Gaps
+
+The following patterns are NOT currently validated by this pass:
+
+1. **Impure values in render**: `Date.now()`, `Math.random()` flowing into render context (handled by `ValidateNoImpureValuesInRender`)
+
+2. **useState/useReducer callbacks**: These hooks call their initializer functions during render, so ref access inside them should error. This requires special hook semantics.
+
+3. **Ref reads during render**: This pass focuses on mutations. Ref reads are handled separately.
+
+## Testing
+
+Test fixtures use naming conventions:
+- `error.*.ts` - Fixtures expected to produce compilation errors
+- Regular names - Fixtures expected to compile successfully
+
+Run tests with:
+```bash
+yarn snap -p <pattern> --nodebug    # Run specific tests
+yarn snap -p <pattern> --nodebug -u # Update expected output
+```

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/access-ref-in-render-mutate-object-with-ref-function.expect.md

@@ -0,0 +1,51 @@
+
+## Input
+
+```javascript
+import {useRef} from 'react';
+
+/**
+ * Allowed: we don't have sufficient type information to be sure that
+ * this accesses an impure value during render.
+ */
+function Component() {
+  const ref = useRef(null);
+  const object = {};
+  object.foo = () => ref.current;
+  const refValue = object.foo();
+  return <div>{refValue}</div>;
+}
+
+```
+
+## Code
+
+```javascript
+import { c as _c } from "react/compiler-runtime";
+import { useRef } from "react";
+
+/**
+ * Allowed: we don't have sufficient type information to be sure that
+ * this accesses an impure value during render.
+ */
+function Component() {
+  const $ = _c(2);
+  const ref = useRef(null);
+  const object = {};
+  object.foo = () => ref.current;
+  const refValue = object.foo();
+  let t0;
+  if ($[0] !== refValue) {
+    t0 = <div>{refValue}</div>;
+    $[0] = refValue;
+    $[1] = t0;
+  } else {
+    t0 = $[1];
+  }
+  return t0;
+}
+
+```
+      
+### Eval output
+(kind: exception) Fixture not implemented

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/access-ref-in-render-mutate-object-with-ref-function.js

@@ -1,5 +1,9 @@
 import {useRef} from 'react';
 
+/**
+ * Allowed: we don't have sufficient type information to be sure that
+ * this accesses an impure value during render.
+ */
 function Component() {
   const ref = useRef(null);
   const object = {};

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/capture-ref-for-mutation.expect.md

@@ -0,0 +1,74 @@
+
+## Input
+
+```javascript
+import {useRef} from 'react';
+import {addOne} from 'shared-runtime';
+
+/**
+ * Allowed: we don't have sufficient type information to be sure that
+ * this accesses an impure value during render.
+ */
+function useKeyCommand() {
+  const currentPosition = useRef(0);
+  const handleKey = direction => () => {
+    const position = currentPosition.current;
+    const nextPosition = direction === 'left' ? addOne(position) : position;
+    currentPosition.current = nextPosition;
+  };
+  const moveLeft = {
+    handler: handleKey('left')(),
+  };
+  const moveRight = {
+    handler: handleKey('right')(),
+  };
+  return [moveLeft, moveRight];
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: useKeyCommand,
+  params: [],
+};
+
+```
+
+## Code
+
+```javascript
+import { c as _c } from "react/compiler-runtime";
+import { useRef } from "react";
+import { addOne } from "shared-runtime";
+
+/**
+ * Allowed: we don't have sufficient type information to be sure that
+ * this accesses an impure value during render.
+ */
+function useKeyCommand() {
+  const $ = _c(1);
+  const currentPosition = useRef(0);
+  let t0;
+  if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
+    const handleKey = (direction) => () => {
+      const position = currentPosition.current;
+      const nextPosition = direction === "left" ? addOne(position) : position;
+      currentPosition.current = nextPosition;
+    };
+    const moveLeft = { handler: handleKey("left")() };
+    const moveRight = { handler: handleKey("right")() };
+    t0 = [moveLeft, moveRight];
+    $[0] = t0;
+  } else {
+    t0 = $[0];
+  }
+  return t0;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: useKeyCommand,
+  params: [],
+};
+
+```
+      
+### Eval output
+(kind: ok) [{},{}]

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/capture-ref-for-mutation.tsx

@@ -1,6 +1,10 @@
 import {useRef} from 'react';
 import {addOne} from 'shared-runtime';
 
+/**
+ * Allowed: we don't have sufficient type information to be sure that
+ * this accesses an impure value during render.
+ */
 function useKeyCommand() {
   const currentPosition = useRef(0);
   const handleKey = direction => () => {

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/capturing-ref-returning-function-in-rendered-object.expect.md

@@ -0,0 +1,60 @@
+
+## Input
+
+```javascript
+import {useRef} from 'react';
+import {Stringify} from 'shared-runtime';
+
+/**
+ * Allowed: we don't have sufficient type information to be sure that
+ * this accesses an impure value during render.
+ */
+function Component(props) {
+  const ref = useRef(props.value);
+  const object = {};
+  object.foo = () => ref.current;
+  return <Stringify object={object} shouldInvokeFns={true} />;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Component,
+  params: [{value: 42}],
+};
+
+```
+
+## Code
+
+```javascript
+import { c as _c } from "react/compiler-runtime";
+import { useRef } from "react";
+import { Stringify } from "shared-runtime";
+
+/**
+ * Allowed: we don't have sufficient type information to be sure that
+ * this accesses an impure value during render.
+ */
+function Component(props) {
+  const $ = _c(1);
+  const ref = useRef(props.value);
+  let t0;
+  if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
+    const object = {};
+    object.foo = () => ref.current;
+    t0 = <Stringify object={object} shouldInvokeFns={true} />;
+    $[0] = t0;
+  } else {
+    t0 = $[0];
+  }
+  return t0;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Component,
+  params: [{ value: 42 }],
+};
+
+```
+      
+### Eval output
+(kind: ok) <div>{"object":{"foo":{"kind":"Function","result":42}},"shouldInvokeFns":true}</div>

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/capturing-ref-returning-function-in-rendered-object.js

@@ -1,6 +1,10 @@
 import {useRef} from 'react';
 import {Stringify} from 'shared-runtime';
 
+/**
+ * Allowed: we don't have sufficient type information to be sure that
+ * this accesses an impure value during render.
+ */
 function Component(props) {
   const ref = useRef(props.value);
   const object = {};

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.capture-ref-for-mutation.expect.md

@@ -1,64 +0,0 @@
-
-## Input
-
-```javascript
-import {useRef} from 'react';
-import {addOne} from 'shared-runtime';
-
-function useKeyCommand() {
-  const currentPosition = useRef(0);
-  const handleKey = direction => () => {
-    const position = currentPosition.current;
-    const nextPosition = direction === 'left' ? addOne(position) : position;
-    currentPosition.current = nextPosition;
-  };
-  const moveLeft = {
-    handler: handleKey('left')(),
-  };
-  const moveRight = {
-    handler: handleKey('right')(),
-  };
-  return [moveLeft, moveRight];
-}
-
-export const FIXTURE_ENTRYPOINT = {
-  fn: useKeyCommand,
-  params: [],
-};
-
-```
-
-
-## Error
-
-```
-Found 2 errors:
-
-Error: Cannot access refs during render
-
-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
-
-error.capture-ref-for-mutation.ts:12:13
-  10 |   };
-  11 |   const moveLeft = {
-> 12 |     handler: handleKey('left')(),
-     |              ^^^^^^^^^^^^^^^^^ This function accesses a ref value
-  13 |   };
-  14 |   const moveRight = {
-  15 |     handler: handleKey('right')(),
-
-Error: Cannot access refs during render
-
-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
-
-error.capture-ref-for-mutation.ts:15:13
-  13 |   };
-  14 |   const moveRight = {
-> 15 |     handler: handleKey('right')(),
-     |              ^^^^^^^^^^^^^^^^^^ This function accesses a ref value
-  16 |   };
-  17 |   return [moveLeft, moveRight];
-  18 | }
-```
-          
-      

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-access-ref-in-reducer.expect.md

@@ -22,7 +22,7 @@ export const FIXTURE_ENTRYPOINT = {
 ## Error
 
 ```
-Found 1 error:
+Found 2 errors:
 
 Error: Cannot access ref value during render
 
@@ -37,6 +37,28 @@ error.invalid-access-ref-in-reducer.ts:5:29
   7 |   return <Stringify state={state} />;
   8 | }
 
+error.invalid-access-ref-in-reducer.ts:5:35
+  3 | function Component(props) {
+  4 |   const ref = useRef(props.value);
+> 5 |   const [state] = useReducer(() => ref.current, null);
+    |                                    ^^^^^^^^^^^ Ref is initially accessed
+  6 |
+  7 |   return <Stringify state={state} />;
+  8 | }
+
+Error: Cannot access ref value during render
+
+React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
+
+error.invalid-access-ref-in-reducer.ts:7:27
+   5 |   const [state] = useReducer(() => ref.current, null);
+   6 |
+>  7 |   return <Stringify state={state} />;
+     |                            ^^^^^ Ref value is used during render
+   8 | }
+   9 |
+  10 | export const FIXTURE_ENTRYPOINT = {
+
 error.invalid-access-ref-in-reducer.ts:5:35
   3 | function Component(props) {
   4 |   const ref = useRef(props.value);

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-access-ref-in-render-mutate-object-with-ref-function.expect.md

@@ -1,45 +0,0 @@
-
-## Input
-
-```javascript
-import {useRef} from 'react';
-
-function Component() {
-  const ref = useRef(null);
-  const object = {};
-  object.foo = () => ref.current;
-  const refValue = object.foo();
-  return <div>{refValue}</div>;
-}
-
-```
-
-
-## Error
-
-```
-Found 1 error:
-
-Error: Cannot access ref value during render
-
-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
-
-error.invalid-access-ref-in-render-mutate-object-with-ref-function.ts:8:15
-   6 |   object.foo = () => ref.current;
-   7 |   const refValue = object.foo();
->  8 |   return <div>{refValue}</div>;
-     |                ^^^^^^^^ Ref value is used during render
-   9 | }
-  10 |
-
-error.invalid-access-ref-in-render-mutate-object-with-ref-function.ts:6:21
-  4 |   const ref = useRef(null);
-  5 |   const object = {};
-> 6 |   object.foo = () => ref.current;
-    |                      ^^^^^^^^^^^ Ref is initially accessed
-  7 |   const refValue = object.foo();
-  8 |   return <div>{refValue}</div>;
-  9 | }
-```
-          
-      

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-access-ref-in-state-initializer.expect.md

@@ -22,7 +22,7 @@ export const FIXTURE_ENTRYPOINT = {
 ## Error
 
 ```
-Found 1 error:
+Found 2 errors:
 
 Error: Cannot access ref value during render
 
@@ -37,6 +37,28 @@ error.invalid-access-ref-in-state-initializer.ts:5:27
   7 |   return <Stringify state={state} />;
   8 | }
 
+error.invalid-access-ref-in-state-initializer.ts:5:33
+  3 | function Component(props) {
+  4 |   const ref = useRef(props.value);
+> 5 |   const [state] = useState(() => ref.current);
+    |                                  ^^^^^^^^^^^ Ref is initially accessed
+  6 |
+  7 |   return <Stringify state={state} />;
+  8 | }
+
+Error: Cannot access ref value during render
+
+React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
+
+error.invalid-access-ref-in-state-initializer.ts:7:27
+   5 |   const [state] = useState(() => ref.current);
+   6 |
+>  7 |   return <Stringify state={state} />;
+     |                            ^^^^^ Ref value is used during render
+   8 | }
+   9 |
+  10 | export const FIXTURE_ENTRYPOINT = {
+
 error.invalid-access-ref-in-state-initializer.ts:5:33
   3 | function Component(props) {
   4 |   const ref = useRef(props.value);

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-capturing-ref-returning-function-in-rendered-object.expect.md

@@ -1,51 +0,0 @@
-
-## Input
-
-```javascript
-import {useRef} from 'react';
-import {Stringify} from 'shared-runtime';
-
-function Component(props) {
-  const ref = useRef(props.value);
-  const object = {};
-  object.foo = () => ref.current;
-  return <Stringify object={object} shouldInvokeFns={true} />;
-}
-
-export const FIXTURE_ENTRYPOINT = {
-  fn: Component,
-  params: [{value: 42}],
-};
-
-```
-
-
-## Error
-
-```
-Found 1 error:
-
-Error: Cannot access ref value during render
-
-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
-
-error.invalid-capturing-ref-returning-function-in-rendered-object.ts:8:28
-   6 |   const object = {};
-   7 |   object.foo = () => ref.current;
->  8 |   return <Stringify object={object} shouldInvokeFns={true} />;
-     |                             ^^^^^^ Ref value is used during render
-   9 | }
-  10 |
-  11 | export const FIXTURE_ENTRYPOINT = {
-
-error.invalid-capturing-ref-returning-function-in-rendered-object.ts:7:21
-   5 |   const ref = useRef(props.value);
-   6 |   const object = {};
->  7 |   object.foo = () => ref.current;
-     |                      ^^^^^^^^^^^ Ref is initially accessed
-   8 |   return <Stringify object={object} shouldInvokeFns={true} />;
-   9 | }
-  10 |
-```
-          
-      

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-disallow-mutating-refs-in-render-transitive.expect.md

@@ -27,14 +27,14 @@ Error: Cannot access refs during render
 
 React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
 
-error.invalid-disallow-mutating-refs-in-render-transitive.ts:9:2
-   7 |   };
-   8 |   const changeRef = setRef;
->  9 |   changeRef();
-     |   ^^^^^^^^^ This function accesses a ref value
-  10 |
-  11 |   return <button ref={ref} />;
-  12 | }
+error.invalid-disallow-mutating-refs-in-render-transitive.ts:6:4
+  4 |
+  5 |   const setRef = () => {
+> 6 |     ref.current = false;
+    |     ^^^^^^^^^^^ Cannot update ref during render
+  7 |   };
+  8 |   const changeRef = setRef;
+  9 |   changeRef();
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-impure-functions-in-render-indirect-via-mutation.expect.md

@@ -6,6 +6,11 @@
 
 import {arrayPush, identity, makeArray} from 'shared-runtime';
 
+/**
+ * Allowed: we don't have sufficient type information to be sure that
+ * this accesses an impure value during render. The impurity is lost
+ * when passed through external function calls.
+ */
 function Component() {
   const getDate = () => Date.now();
   const now = getDate();
@@ -26,22 +31,22 @@ Error: Cannot access impure value during render
 
 Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent).
 
-error.invalid-impure-functions-in-render-indirect-via-mutation.ts:10:23
-   8 |   const array = [];
-   9 |   arrayPush(array, now);
-> 10 |   return <Foo hasDate={array} />;
+error.invalid-impure-functions-in-render-indirect-via-mutation.ts:15:23
+  13 |   const array = [];
+  14 |   arrayPush(array, now);
+> 15 |   return <Foo hasDate={array} />;
      |                        ^^^^^ Cannot access impure value during render
-  11 | }
-  12 |
+  16 | }
+  17 |
 
-error.invalid-impure-functions-in-render-indirect-via-mutation.ts:6:24
-  4 |
-  5 | function Component() {
-> 6 |   const getDate = () => Date.now();
-    |                         ^^^^^^^^^^ `Date.now` is an impure function.
-  7 |   const now = getDate();
-  8 |   const array = [];
-  9 |   arrayPush(array, now);
+error.invalid-impure-functions-in-render-indirect-via-mutation.ts:11:24
+   9 |  */
+  10 | function Component() {
+> 11 |   const getDate = () => Date.now();
+     |                         ^^^^^^^^^^ `Date.now` is an impure function.
+  12 |   const now = getDate();
+  13 |   const array = [];
+  14 |   arrayPush(array, now);
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-impure-functions-in-render-indirect-via-mutation.js

@@ -2,6 +2,11 @@
 
 import {arrayPush, identity, makeArray} from 'shared-runtime';
 
+/**
+ * Allowed: we don't have sufficient type information to be sure that
+ * this accesses an impure value during render. The impurity is lost
+ * when passed through external function calls.
+ */
 function Component() {
   const getDate = () => Date.now();
   const now = getDate();

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-impure-functions-in-render-indirect.expect.md

@@ -1,46 +0,0 @@
-
-## Input
-
-```javascript
-// @validateNoImpureFunctionsInRender
-
-import {identity, makeArray} from 'shared-runtime';
-
-function Component() {
-  const getDate = () => Date.now();
-  const array = makeArray(getDate());
-  const hasDate = identity(array);
-  return <Foo hasDate={hasDate} />;
-}
-
-```
-
-
-## Error
-
-```
-Found 1 error:
-
-Error: Cannot access impure value during render
-
-Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent).
-
-error.invalid-impure-functions-in-render-indirect.ts:9:23
-   7 |   const array = makeArray(getDate());
-   8 |   const hasDate = identity(array);
->  9 |   return <Foo hasDate={hasDate} />;
-     |                        ^^^^^^^ Cannot access impure value during render
-  10 | }
-  11 |
-
-error.invalid-impure-functions-in-render-indirect.ts:6:24
-  4 |
-  5 | function Component() {
-> 6 |   const getDate = () => Date.now();
-    |                         ^^^^^^^^^^ `Date.now` is an impure function.
-  7 |   const array = makeArray(getDate());
-  8 |   const hasDate = identity(array);
-  9 |   return <Foo hasDate={hasDate} />;
-```
-          
-      

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-impure-functions-in-render-via-function-call-2.expect.md

@@ -1,52 +0,0 @@
-
-## Input
-
-```javascript
-// @validateNoImpureFunctionsInRender
-
-import {identity, makeArray} from 'shared-runtime';
-
-function Component() {
-  const now = () => Date.now();
-  const f = () => {
-    // this should error but we currently lose track of the impurity bc
-    // the impure value comes from behind a call
-    const array = makeArray(now());
-    const hasDate = identity(array);
-    return hasDate;
-  };
-  const hasDate = f();
-  return <Foo hasDate={hasDate} />;
-}
-
-```
-
-
-## Error
-
-```
-Found 1 error:
-
-Error: Cannot access impure value during render
-
-Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent).
-
-error.invalid-impure-functions-in-render-via-function-call-2.ts:15:23
-  13 |   };
-  14 |   const hasDate = f();
-> 15 |   return <Foo hasDate={hasDate} />;
-     |                        ^^^^^^^ Cannot access impure value during render
-  16 | }
-  17 |
-
-error.invalid-impure-functions-in-render-via-function-call-2.ts:6:20
-  4 |
-  5 | function Component() {
-> 6 |   const now = () => Date.now();
-    |                     ^^^^^^^^^^ `Date.now` is an impure function.
-  7 |   const f = () => {
-  8 |     // this should error but we currently lose track of the impurity bc
-  9 |     // the impure value comes from behind a call
-```
-          
-      

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-impure-functions-in-render-via-render-helper-typed.expect.md

@@ -7,7 +7,7 @@
 import {typedArrayPush, typedIdentity} from 'shared-runtime';
 
 function Component() {
-  const now = Date.now();
+  const now = () => Date.now();
   const renderItem = () => {
     const array = [];
     typedArrayPush(array, now());
@@ -29,19 +29,20 @@ Error: Cannot access impure value during render
 
 Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent).
 
-error.invalid-impure-functions-in-render-via-render-helper-typed.ts:13:26
-  11 |     return <Bar hasDate={hasDate} />;
+error.invalid-impure-functions-in-render-via-render-helper-typed.ts:11:25
+   9 |     typedArrayPush(array, now());
+  10 |     const hasDate = typedIdentity(array);
+> 11 |     return <Bar hasDate={hasDate} />;
+     |                          ^^^^^^^ Cannot access impure value during render
   12 |   };
-> 13 |   return <Foo renderItem={renderItem} />;
-     |                           ^^^^^^^^^^ Cannot access impure value during render
+  13 |   return <Foo renderItem={renderItem} />;
   14 | }
-  15 |
 
-error.invalid-impure-functions-in-render-via-render-helper-typed.ts:6:14
+error.invalid-impure-functions-in-render-via-render-helper-typed.ts:6:20
   4 |
   5 | function Component() {
-> 6 |   const now = Date.now();
-    |               ^^^^^^^^^^ `Date.now` is an impure function.
+> 6 |   const now = () => Date.now();
+    |                     ^^^^^^^^^^ `Date.now` is an impure function.
   7 |   const renderItem = () => {
   8 |     const array = [];
   9 |     typedArrayPush(array, now());

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-impure-functions-in-render-via-render-helper-typed.js

@@ -3,7 +3,7 @@
 import {typedArrayPush, typedIdentity} from 'shared-runtime';
 
 function Component() {
-  const now = Date.now();
+  const now = () => Date.now();
   const renderItem = () => {
     const array = [];
     typedArrayPush(array, now());

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-impure-functions-in-render-via-render-helper.expect.md

@@ -1,49 +0,0 @@
-
-## Input
-
-```javascript
-// @validateNoImpureFunctionsInRender
-
-import {identity, makeArray} from 'shared-runtime';
-
-function Component() {
-  const now = Date.now();
-  const renderItem = () => {
-    const array = makeArray(now);
-    const hasDate = identity(array);
-    return <Bar hasDate={hasDate} />;
-  };
-  return <Foo renderItem={renderItem} />;
-}
-
-```
-
-
-## Error
-
-```
-Found 1 error:
-
-Error: Cannot access impure value during render
-
-Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent).
-
-error.invalid-impure-functions-in-render-via-render-helper.ts:12:26
-  10 |     return <Bar hasDate={hasDate} />;
-  11 |   };
-> 12 |   return <Foo renderItem={renderItem} />;
-     |                           ^^^^^^^^^^ Cannot access impure value during render
-  13 | }
-  14 |
-
-error.invalid-impure-functions-in-render-via-render-helper.ts:6:14
-  4 |
-  5 | function Component() {
-> 6 |   const now = Date.now();
-    |               ^^^^^^^^^^ `Date.now` is an impure function.
-  7 |   const renderItem = () => {
-  8 |     const array = makeArray(now);
-  9 |     const hasDate = identity(array);
-```
-          
-      

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-impure-value-in-render-helper.expect.md

@@ -17,7 +17,7 @@ function Component() {
 ## Error
 
 ```
-Found 1 error:
+Found 2 errors:
 
 Error: Cannot access impure value during render
 
@@ -32,6 +32,27 @@ error.invalid-impure-value-in-render-helper.ts:5:17
   7 |   return <div>{render()}</div>;
   8 | }
 
+error.invalid-impure-value-in-render-helper.ts:3:20
+  1 | // @validateNoImpureFunctionsInRender
+  2 | function Component() {
+> 3 |   const now = () => Date.now();
+    |                     ^^^^^^^^^^ `Date.now` is an impure function.
+  4 |   const render = () => {
+  5 |     return <div>{now()}</div>;
+  6 |   };
+
+Error: Cannot access impure value during render
+
+Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent).
+
+error.invalid-impure-value-in-render-helper.ts:7:15
+  5 |     return <div>{now()}</div>;
+  6 |   };
+> 7 |   return <div>{render()}</div>;
+    |                ^^^^^^^^ Cannot access impure value during render
+  8 | }
+  9 |
+
 error.invalid-impure-value-in-render-helper.ts:3:20
   1 | // @validateNoImpureFunctionsInRender
   2 | function Component() {

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-pass-ref-to-function.expect.md

@@ -1,34 +0,0 @@
-
-## Input
-
-```javascript
-// @validateRefAccessDuringRender
-function Component(props) {
-  const ref = useRef(null);
-  const x = foo(ref);
-  return x.current;
-}
-
-```
-
-
-## Error
-
-```
-Found 1 error:
-
-Error: Cannot access refs during render
-
-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
-
-error.invalid-pass-ref-to-function.ts:4:16
-  2 | function Component(props) {
-  3 |   const ref = useRef(null);
-> 4 |   const x = foo(ref);
-    |                 ^^^ Passing a ref to a function may read its value during render
-  5 |   return x.current;
-  6 | }
-  7 |
-```
-          
-      

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-pass-ref-to-function.js

@@ -1,6 +0,0 @@
-// @validateRefAccessDuringRender
-function Component(props) {
-  const ref = useRef(null);
-  const x = foo(ref);
-  return x.current;
-}

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-ref-initialization-unary-not.expect.md

@@ -29,15 +29,13 @@ Error: Cannot access refs during render
 
 React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
 
-  4 | component C() {
-  5 |   const r = useRef(null);
-> 6 |   if (!r.current) {
-    |        ^^^^^^^^^ Cannot access ref value during render
-  7 |     r.current = 1;
-  8 |   }
-  9 | }
-
-To initialize a ref only once, check that the ref is null with the pattern `if (ref.current == null) { ref.current = ... }`
+   5 |   const r = useRef(null);
+   6 |   if (!r.current) {
+>  7 |     r.current = 1;
+     |     ^^^^^^^^^ Cannot update ref during render
+   8 |   }
+   9 | }
+  10 |
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-use-ref-added-to-dep-without-type-info.expect.md

@@ -1,53 +0,0 @@
-
-## Input
-
-```javascript
-// @validateRefAccessDuringRender
-function Foo({a}) {
-  const ref = useRef();
-  // type information is lost here as we don't track types of fields
-  const val = {ref};
-  // without type info, we don't know that val.ref.current is a ref value so we
-  // *would* end up depending on val.ref.current
-  // however, this is an instance of accessing a ref during render and is disallowed
-  // under React's rules, so we reject this input
-  const x = {a, val: val.ref.current};
-
-  return <VideoList videos={x} />;
-}
-
-```
-
-
-## Error
-
-```
-Found 2 errors:
-
-Error: Cannot access refs during render
-
-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
-
-error.invalid-use-ref-added-to-dep-without-type-info.ts:10:21
-   8 |   // however, this is an instance of accessing a ref during render and is disallowed
-   9 |   // under React's rules, so we reject this input
-> 10 |   const x = {a, val: val.ref.current};
-     |                      ^^^^^^^^^^^^^^^ Cannot access ref value during render
-  11 |
-  12 |   return <VideoList videos={x} />;
-  13 | }
-
-Error: Cannot access refs during render
-
-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
-
-error.invalid-use-ref-added-to-dep-without-type-info.ts:12:28
-  10 |   const x = {a, val: val.ref.current};
-  11 |
-> 12 |   return <VideoList videos={x} />;
-     |                             ^ Cannot access ref value during render
-  13 | }
-  14 |
-```
-          
-      

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-use-ref-added-to-dep-without-type-info.js

@@ -1,13 +0,0 @@
-// @validateRefAccessDuringRender
-function Foo({a}) {
-  const ref = useRef();
-  // type information is lost here as we don't track types of fields
-  const val = {ref};
-  // without type info, we don't know that val.ref.current is a ref value so we
-  // *would* end up depending on val.ref.current
-  // however, this is an instance of accessing a ref during render and is disallowed
-  // under React's rules, so we reject this input
-  const x = {a, val: val.ref.current};
-
-  return <VideoList videos={x} />;
-}

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.ref-initialization-call-2.expect.md

@@ -1,41 +0,0 @@
-
-## Input
-
-```javascript
-//@flow
-import {useRef} from 'react';
-
-component C() {
-  const r = useRef(null);
-  if (r.current == null) {
-    f(r);
-  }
-}
-
-export const FIXTURE_ENTRYPOINT = {
-  fn: C,
-  params: [{}],
-};
-
-```
-
-
-## Error
-
-```
-Found 1 error:
-
-Error: Cannot access refs during render
-
-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
-
-   5 |   const r = useRef(null);
-   6 |   if (r.current == null) {
->  7 |     f(r);
-     |       ^ Passing a ref to a function may read its value during render
-   8 |   }
-   9 | }
-  10 |
-```
-          
-      

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.ref-initialization-call.expect.md

@@ -1,41 +0,0 @@
-
-## Input
-
-```javascript
-//@flow
-import {useRef} from 'react';
-
-component C() {
-  const r = useRef(null);
-  if (r.current == null) {
-    f(r.current);
-  }
-}
-
-export const FIXTURE_ENTRYPOINT = {
-  fn: C,
-  params: [{}],
-};
-
-```
-
-
-## Error
-
-```
-Found 1 error:
-
-Error: Cannot access refs during render
-
-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
-
-   5 |   const r = useRef(null);
-   6 |   if (r.current == null) {
->  7 |     f(r.current);
-     |       ^^^^^^^^^ Passing a ref to a function may read its value during render
-   8 |   }
-   9 | }
-  10 |
-```
-          
-      

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.ref-initialization-linear.expect.md

@@ -33,10 +33,18 @@ React refs are values that are not needed for rendering. Refs should only be acc
    6 |   if (r.current == null) {
    7 |     r.current = 42;
 >  8 |     r.current = 42;
-     |     ^^^^^^^^^ Cannot update ref during render
+     |     ^^^^^^^^^ Ref is initialized more than once during render
    9 |   }
   10 | }
   11 |
+
+   5 |   const r = useRef(null);
+   6 |   if (r.current == null) {
+>  7 |     r.current = 42;
+     |     ^^^^^^^^^ Ref was first initialized here
+   8 |     r.current = 42;
+   9 |   }
+  10 | }
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.ref-initialization-nonif.expect.md

@@ -24,31 +24,19 @@ export const FIXTURE_ENTRYPOINT = {
 ## Error
 
 ```
-Found 2 errors:
+Found 1 error:
 
 Error: Cannot access refs during render
 
 React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
 
-  4 | component C() {
-  5 |   const r = useRef(null);
-> 6 |   const guard = r.current == null;
-    |                 ^^^^^^^^^^^^^^^^^ Cannot access ref value during render
-  7 |   if (guard) {
-  8 |     r.current = 1;
-  9 |   }
-
-Error: Cannot access refs during render
-
-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
-
-   5 |   const r = useRef(null);
    6 |   const guard = r.current == null;
->  7 |   if (guard) {
-     |       ^^^^^ Cannot access ref value during render
-   8 |     r.current = 1;
+   7 |   if (guard) {
+>  8 |     r.current = 1;
+     |     ^^^^^^^^^ Cannot update ref during render
    9 |   }
   10 | }
+  11 |
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.ref-initialization-post-access-2.expect.md

@@ -1,42 +0,0 @@
-
-## Input
-
-```javascript
-//@flow
-import {useRef} from 'react';
-
-component C() {
-  const r = useRef(null);
-  if (r.current == null) {
-    r.current = 1;
-  }
-  f(r.current);
-}
-
-export const FIXTURE_ENTRYPOINT = {
-  fn: C,
-  params: [{}],
-};
-
-```
-
-
-## Error
-
-```
-Found 1 error:
-
-Error: Cannot access refs during render
-
-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
-
-   7 |     r.current = 1;
-   8 |   }
->  9 |   f(r.current);
-     |     ^^^^^^^^^ Passing a ref to a function may read its value during render
-  10 | }
-  11 |
-  12 | export const FIXTURE_ENTRYPOINT = {
-```
-          
-      

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.ref-value-in-custom-component-event-handler-wrapper.expect.md

@@ -1,69 +0,0 @@
-
-## Input
-
-```javascript
-// @enableInferEventHandlers
-import {useRef} from 'react';
-
-// Simulates a custom component wrapper
-function CustomForm({onSubmit, children}: any) {
-  return <form onSubmit={onSubmit}>{children}</form>;
-}
-
-// Simulates react-hook-form's handleSubmit
-function handleSubmit<T>(callback: (data: T) => void) {
-  return (event: any) => {
-    event.preventDefault();
-    callback({} as T);
-  };
-}
-
-function Component() {
-  const ref = useRef<HTMLInputElement>(null);
-
-  const onSubmit = (data: any) => {
-    // This should error: passing function with ref access to custom component
-    // event handler, even though it would be safe on a native <form>
-    if (ref.current !== null) {
-      console.log(ref.current.value);
-    }
-  };
-
-  return (
-    <>
-      <input ref={ref} />
-      <CustomForm onSubmit={handleSubmit(onSubmit)}>
-        <button type="submit">Submit</button>
-      </CustomForm>
-    </>
-  );
-}
-
-export const FIXTURE_ENTRYPOINT = {
-  fn: Component,
-  params: [{}],
-};
-
-```
-
-
-## Error
-
-```
-Found 1 error:
-
-Error: Cannot access refs during render
-
-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
-
-error.ref-value-in-custom-component-event-handler-wrapper.ts:31:41
-  29 |     <>
-  30 |       <input ref={ref} />
-> 31 |       <CustomForm onSubmit={handleSubmit(onSubmit)}>
-     |                                          ^^^^^^^^ Passing a ref to a function may read its value during render
-  32 |         <button type="submit">Submit</button>
-  33 |       </CustomForm>
-  34 |     </>
-```
-          
-      

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.ref-value-in-event-handler-wrapper.expect.md

@@ -1,64 +0,0 @@
-
-## Input
-
-```javascript
-// @enableInferEventHandlers
-import {useRef} from 'react';
-
-// Simulates a handler wrapper
-function handleClick(value: any) {
-  return () => {
-    console.log(value);
-  };
-}
-
-function Component() {
-  const ref = useRef(null);
-
-  // This should still error: passing ref.current directly to a wrapper
-  // The ref value is accessed during render, not in the event handler
-  return (
-    <>
-      <input ref={ref} />
-      <button onClick={handleClick(ref.current)}>Click</button>
-    </>
-  );
-}
-
-export const FIXTURE_ENTRYPOINT = {
-  fn: Component,
-  params: [{}],
-};
-
-```
-
-
-## Error
-
-```
-Found 1 error:
-
-Error: Cannot access ref value during render
-
-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
-
-error.ref-value-in-event-handler-wrapper.ts:19:6
-  17 |     <>
-  18 |       <input ref={ref} />
-> 19 |       <button onClick={handleClick(ref.current)}>Click</button>
-     |       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Ref value is used during render
-  20 |     </>
-  21 |   );
-  22 | }
-
-error.ref-value-in-event-handler-wrapper.ts:19:35
-  17 |     <>
-  18 |       <input ref={ref} />
-> 19 |       <button onClick={handleClick(ref.current)}>Click</button>
-     |                                    ^^^^^^^^^^^ Ref is initially accessed
-  20 |     </>
-  21 |   );
-  22 | }
-```
-          
-      

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.todo-useCallback-set-ref-nested-property-ref-modified-later-preserve-memoization.expect.md

@@ -41,7 +41,7 @@ error.todo-useCallback-set-ref-nested-property-ref-modified-later-preserve-memoi
   12 |
   13 |   // The ref is modified later, extending its range and preventing memoization of onChange
 > 14 |   ref.current.inner = null;
-     |   ^^^^^^^^^^^ Cannot update ref during render
+     |   ^^^^^^^^^^^^^^^^^ Cannot update ref during render
   15 |
   16 |   return <input onChange={onChange} />;
   17 | }

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.useCallback-accesses-ref-mutated-later-via-function-preserve-memoization.expect.md

@@ -40,14 +40,14 @@ Error: Cannot access refs during render
 
 React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
 
-error.useCallback-accesses-ref-mutated-later-via-function-preserve-memoization.ts:17:2
-  15 |     ref.current.inner = null;
+error.useCallback-accesses-ref-mutated-later-via-function-preserve-memoization.ts:15:4
+  13 |   // The ref is modified later, extending its range and preventing memoization of onChange
+  14 |   const reset = () => {
+> 15 |     ref.current.inner = null;
+     |     ^^^^^^^^^^^^^^^^^ Cannot update ref during render
   16 |   };
-> 17 |   reset();
-     |   ^^^^^ This function accesses a ref value
+  17 |   reset();
   18 |
-  19 |   return <input onChange={onChange} />;
-  20 | }
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.useCallback-set-ref-nested-property-dont-preserve-memoization.expect.md

@@ -40,7 +40,7 @@ error.useCallback-set-ref-nested-property-dont-preserve-memoization.ts:13:2
   11 |   });
   12 |
 > 13 |   ref.current.inner = null;
-     |   ^^^^^^^^^^^ Cannot update ref during render
+     |   ^^^^^^^^^^^^^^^^^ Cannot update ref during render
   14 |
   15 |   return <input onChange={onChange} />;
   16 | }

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.validate-mutate-ref-arg-in-render.expect.md

@@ -1,39 +0,0 @@
-
-## Input
-
-```javascript
-// @validateRefAccessDuringRender:true
-function Foo(props, ref) {
-  console.log(ref.current);
-  return <div>{props.bar}</div>;
-}
-
-export const FIXTURE_ENTRYPOINT = {
-  fn: Foo,
-  params: [{bar: 'foo'}, {ref: {cuurrent: 1}}],
-  isComponent: true,
-};
-
-```
-
-
-## Error
-
-```
-Found 1 error:
-
-Error: Cannot access refs during render
-
-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
-
-error.validate-mutate-ref-arg-in-render.ts:3:14
-  1 | // @validateRefAccessDuringRender:true
-  2 | function Foo(props, ref) {
-> 3 |   console.log(ref.current);
-    |               ^^^^^^^^^^^ Passing a ref to a function may read its value during render
-  4 |   return <div>{props.bar}</div>;
-  5 | }
-  6 |
-```
-          
-      

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/impure-functions-in-render-indirect.expect.md

@@ -0,0 +1,56 @@
+
+## Input
+
+```javascript
+// @validateNoImpureFunctionsInRender
+
+import {identity, makeArray} from 'shared-runtime';
+
+/**
+ * Allowed: we don't have sufficient type information to be sure that
+ * this accesses an impure value during render. The impurity is lost
+ * when passed through external function calls.
+ */
+function Component() {
+  const getDate = () => Date.now();
+  const array = makeArray(getDate());
+  const hasDate = identity(array);
+  return <Foo hasDate={hasDate} />;
+}
+
+```
+
+## Code
+
+```javascript
+import { c as _c } from "react/compiler-runtime"; // @validateNoImpureFunctionsInRender
+
+import { identity, makeArray } from "shared-runtime";
+
+/**
+ * Allowed: we don't have sufficient type information to be sure that
+ * this accesses an impure value during render. The impurity is lost
+ * when passed through external function calls.
+ */
+function Component() {
+  const $ = _c(1);
+  const getDate = _temp;
+  let t0;
+  if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
+    const array = makeArray(getDate());
+    const hasDate = identity(array);
+    t0 = <Foo hasDate={hasDate} />;
+    $[0] = t0;
+  } else {
+    t0 = $[0];
+  }
+  return t0;
+}
+function _temp() {
+  return Date.now();
+}
+
+```
+      
+### Eval output
+(kind: exception) Fixture not implemented

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/impure-functions-in-render-indirect.js

@@ -2,6 +2,11 @@
 
 import {identity, makeArray} from 'shared-runtime';
 
+/**
+ * Allowed: we don't have sufficient type information to be sure that
+ * this accesses an impure value during render. The impurity is lost
+ * when passed through external function calls.
+ */
 function Component() {
   const getDate = () => Date.now();
   const array = makeArray(getDate());

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/impure-functions-in-render-via-function-call-2.expect.md

@@ -0,0 +1,64 @@
+
+## Input
+
+```javascript
+// @validateNoImpureFunctionsInRender
+
+import {identity, makeArray} from 'shared-runtime';
+
+/**
+ * Allowed: we don't have sufficient type information to be sure that
+ * this accesses an impure value during render. The impurity is lost
+ * when passed through external function calls.
+ */
+function Component() {
+  const now = () => Date.now();
+  const f = () => {
+    const array = makeArray(now());
+    const hasDate = identity(array);
+    return hasDate;
+  };
+  const hasDate = f();
+  return <Foo hasDate={hasDate} />;
+}
+
+```
+
+## Code
+
+```javascript
+import { c as _c } from "react/compiler-runtime"; // @validateNoImpureFunctionsInRender
+
+import { identity, makeArray } from "shared-runtime";
+
+/**
+ * Allowed: we don't have sufficient type information to be sure that
+ * this accesses an impure value during render. The impurity is lost
+ * when passed through external function calls.
+ */
+function Component() {
+  const $ = _c(1);
+  const now = _temp;
+  let t0;
+  if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
+    const f = () => {
+      const array = makeArray(now());
+      const hasDate = identity(array);
+      return hasDate;
+    };
+    const hasDate_0 = f();
+    t0 = <Foo hasDate={hasDate_0} />;
+    $[0] = t0;
+  } else {
+    t0 = $[0];
+  }
+  return t0;
+}
+function _temp() {
+  return Date.now();
+}
+
+```
+      
+### Eval output
+(kind: exception) Fixture not implemented

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/impure-functions-in-render-via-function-call-2.js

@@ -2,11 +2,14 @@
 
 import {identity, makeArray} from 'shared-runtime';
 
+/**
+ * Allowed: we don't have sufficient type information to be sure that
+ * this accesses an impure value during render. The impurity is lost
+ * when passed through external function calls.
+ */
 function Component() {
   const now = () => Date.now();
   const f = () => {
-    // this should error but we currently lose track of the impurity bc
-    // the impure value comes from behind a call
     const array = makeArray(now());
     const hasDate = identity(array);
     return hasDate;

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/infer-effect-dependencies/bailout-retry/mutate-after-useeffect-ref-access.expect.md

@@ -47,7 +47,7 @@ export const FIXTURE_ENTRYPOINT = {
 ## Logs
 
 ```
-{"kind":"CompileError","fnLoc":{"start":{"line":6,"column":0,"index":158},"end":{"line":11,"column":1,"index":331},"filename":"mutate-after-useeffect-ref-access.ts"},"detail":{"options":{"category":"Refs","reason":"Cannot access refs during render","description":"React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef)","details":[{"kind":"error","loc":{"start":{"line":9,"column":2,"index":289},"end":{"line":9,"column":16,"index":303},"filename":"mutate-after-useeffect-ref-access.ts"},"message":"Cannot update ref during render"}]}}}
+{"kind":"CompileError","fnLoc":{"start":{"line":6,"column":0,"index":158},"end":{"line":11,"column":1,"index":331},"filename":"mutate-after-useeffect-ref-access.ts"},"detail":{"options":{"category":"Refs","reason":"Cannot access refs during render","description":"React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef)","details":[{"kind":"error","loc":{"start":{"line":9,"column":2,"index":289},"end":{"line":9,"column":20,"index":307},"filename":"mutate-after-useeffect-ref-access.ts"},"message":"Cannot update ref during render"}]}}}
 {"kind":"AutoDepsDecorations","fnLoc":{"start":{"line":8,"column":2,"index":237},"end":{"line":8,"column":50,"index":285},"filename":"mutate-after-useeffect-ref-access.ts"},"decorations":[{"start":{"line":8,"column":24,"index":259},"end":{"line":8,"column":30,"index":265},"filename":"mutate-after-useeffect-ref-access.ts","identifierName":"arrRef"}]}
 {"kind":"CompileSuccess","fnLoc":{"start":{"line":6,"column":0,"index":158},"end":{"line":11,"column":1,"index":331},"filename":"mutate-after-useeffect-ref-access.ts"},"fnName":"Component","memoSlots":0,"memoBlocks":0,"memoValues":0,"prunedMemoBlocks":0,"prunedMemoValues":0}
 ```

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/new-mutability/mutate-after-useeffect-ref-access.expect.md

@@ -47,7 +47,7 @@ export const FIXTURE_ENTRYPOINT = {
 ## Logs
 
 ```
-{"kind":"CompileError","fnLoc":{"start":{"line":6,"column":0,"index":190},"end":{"line":11,"column":1,"index":363},"filename":"mutate-after-useeffect-ref-access.ts"},"detail":{"options":{"category":"Refs","reason":"Cannot access refs during render","description":"React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef)","details":[{"kind":"error","loc":{"start":{"line":9,"column":2,"index":321},"end":{"line":9,"column":16,"index":335},"filename":"mutate-after-useeffect-ref-access.ts"},"message":"Cannot update ref during render"}]}}}
+{"kind":"CompileError","fnLoc":{"start":{"line":6,"column":0,"index":190},"end":{"line":11,"column":1,"index":363},"filename":"mutate-after-useeffect-ref-access.ts"},"detail":{"options":{"category":"Refs","reason":"Cannot access refs during render","description":"React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef)","details":[{"kind":"error","loc":{"start":{"line":9,"column":2,"index":321},"end":{"line":9,"column":20,"index":339},"filename":"mutate-after-useeffect-ref-access.ts"},"message":"Cannot update ref during render"}]}}}
 {"kind":"AutoDepsDecorations","fnLoc":{"start":{"line":8,"column":2,"index":269},"end":{"line":8,"column":50,"index":317},"filename":"mutate-after-useeffect-ref-access.ts"},"decorations":[{"start":{"line":8,"column":24,"index":291},"end":{"line":8,"column":30,"index":297},"filename":"mutate-after-useeffect-ref-access.ts","identifierName":"arrRef"}]}
 {"kind":"CompileSuccess","fnLoc":{"start":{"line":6,"column":0,"index":190},"end":{"line":11,"column":1,"index":363},"filename":"mutate-after-useeffect-ref-access.ts"},"fnName":"Component","memoSlots":0,"memoBlocks":0,"memoValues":0,"prunedMemoBlocks":0,"prunedMemoValues":0}
 ```

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/pass-ref-to-function.expect.md

@@ -0,0 +1,45 @@
+
+## Input
+
+```javascript
+// @validateRefAccessDuringRender
+
+/**
+ * Allowed: we don't have sufficient type information to be sure that
+ * this accesses a ref during render. The return type of foo() is unknown.
+ */
+function Component(props) {
+  const ref = useRef(null);
+  const x = foo(ref);
+  return x.current;
+}
+
+```
+
+## Code
+
+```javascript
+import { c as _c } from "react/compiler-runtime"; // @validateRefAccessDuringRender
+
+/**
+ * Allowed: we don't have sufficient type information to be sure that
+ * this accesses a ref during render. The return type of foo() is unknown.
+ */
+function Component(props) {
+  const $ = _c(1);
+  const ref = useRef(null);
+  let t0;
+  if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
+    t0 = foo(ref);
+    $[0] = t0;
+  } else {
+    t0 = $[0];
+  }
+  const x = t0;
+  return x.current;
+}
+
+```
+      
+### Eval output
+(kind: exception) Fixture not implemented

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/pass-ref-to-function.js

@@ -0,0 +1,11 @@
+// @validateRefAccessDuringRender
+
+/**
+ * Allowed: we don't have sufficient type information to be sure that
+ * this accesses a ref during render. The return type of foo() is unknown.
+ */
+function Component(props) {
+  const ref = useRef(null);
+  const x = foo(ref);
+  return x.current;
+}

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/preserve-memo-validation/error.maybe-mutable-ref-not-preserved.expect.md

@@ -1,42 +0,0 @@
-
-## Input
-
-```javascript
-// @validatePreserveExistingMemoizationGuarantees:true
-
-import {useRef, useMemo} from 'react';
-import {makeArray} from 'shared-runtime';
-
-function useFoo() {
-  const r = useRef();
-  return useMemo(() => makeArray(r), []);
-}
-
-export const FIXTURE_ENTRYPOINT = {
-  fn: useFoo,
-  params: [],
-};
-
-```
-
-
-## Error
-
-```
-Found 1 error:
-
-Error: Cannot access refs during render
-
-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
-
-error.maybe-mutable-ref-not-preserved.ts:8:33
-   6 | function useFoo() {
-   7 |   const r = useRef();
->  8 |   return useMemo(() => makeArray(r), []);
-     |                                  ^ Passing a ref to a function may read its value during render
-   9 | }
-  10 |
-  11 | export const FIXTURE_ENTRYPOINT = {
-```
-          
-      

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/preserve-memo-validation/error.useMemo-with-refs.flow.expect.md

@@ -1,37 +0,0 @@
-
-## Input
-
-```javascript
-// @flow @validatePreserveExistingMemoizationGuarantees
-import {identity} from 'shared-runtime';
-
-component Component(disableLocalRef, ref) {
-  const localRef = useFooRef();
-  const mergedRef = useMemo(() => {
-    return disableLocalRef ? ref : identity(ref, localRef);
-  }, [disableLocalRef, ref, localRef]);
-  return <div ref={mergedRef} />;
-}
-
-```
-
-
-## Error
-
-```
-Found 1 error:
-
-Error: Cannot access refs during render
-
-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
-
-   5 |   const localRef = useFooRef();
-   6 |   const mergedRef = useMemo(() => {
->  7 |     return disableLocalRef ? ref : identity(ref, localRef);
-     |                                             ^^^ Passing a ref to a function may read its value during render
-   8 |   }, [disableLocalRef, ref, localRef]);
-   9 |   return <div ref={mergedRef} />;
-  10 | }
-```
-          
-      

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/preserve-memo-validation/maybe-mutable-ref-not-preserved.expect.md

@@ -0,0 +1,59 @@
+
+## Input
+
+```javascript
+// @validatePreserveExistingMemoizationGuarantees:true
+
+import {useRef, useMemo} from 'react';
+import {makeArray} from 'shared-runtime';
+
+/**
+ * Allowed: we don't have sufficient type information to be sure that
+ * this accesses an impure value during render.
+ */
+function useFoo() {
+  const r = useRef();
+  return useMemo(() => makeArray(r), []);
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: useFoo,
+  params: [],
+};
+
+```
+
+## Code
+
+```javascript
+import { c as _c } from "react/compiler-runtime"; // @validatePreserveExistingMemoizationGuarantees:true
+
+import { useRef, useMemo } from "react";
+import { makeArray } from "shared-runtime";
+
+/**
+ * Allowed: we don't have sufficient type information to be sure that
+ * this accesses an impure value during render.
+ */
+function useFoo() {
+  const $ = _c(1);
+  const r = useRef();
+  let t0;
+  if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
+    t0 = makeArray(r);
+    $[0] = t0;
+  } else {
+    t0 = $[0];
+  }
+  return t0;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: useFoo,
+  params: [],
+};
+
+```
+      
+### Eval output
+(kind: ok) [{}]

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/preserve-memo-validation/maybe-mutable-ref-not-preserved.ts

@@ -3,6 +3,10 @@
 import {useRef, useMemo} from 'react';
 import {makeArray} from 'shared-runtime';
 
+/**
+ * Allowed: we don't have sufficient type information to be sure that
+ * this accesses an impure value during render.
+ */
 function useFoo() {
   const r = useRef();
   return useMemo(() => makeArray(r), []);

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/preserve-memo-validation/useMemo-with-refs.flow.expect.md

@@ -0,0 +1,52 @@
+
+## Input
+
+```javascript
+// @flow @validatePreserveExistingMemoizationGuarantees
+import {identity} from 'shared-runtime';
+
+component Component(disableLocalRef, ref) {
+  const localRef = useFooRef();
+  const mergedRef = useMemo(() => {
+    return disableLocalRef ? ref : identity(ref, localRef);
+  }, [disableLocalRef, ref, localRef]);
+  return <div ref={mergedRef} />;
+}
+
+```
+
+## Code
+
+```javascript
+import { c as _c } from "react/compiler-runtime";
+import { identity } from "shared-runtime";
+
+const Component = React.forwardRef(Component_withRef);
+function Component_withRef(t0, ref) {
+  const $ = _c(6);
+  const { disableLocalRef } = t0;
+  const localRef = useFooRef();
+  let t1;
+  if ($[0] !== disableLocalRef || $[1] !== localRef || $[2] !== ref) {
+    t1 = disableLocalRef ? ref : identity(ref, localRef);
+    $[0] = disableLocalRef;
+    $[1] = localRef;
+    $[2] = ref;
+    $[3] = t1;
+  } else {
+    t1 = $[3];
+  }
+  const mergedRef = t1;
+  let t2;
+  if ($[4] !== mergedRef) {
+    t2 = <div ref={mergedRef} />;
+    $[4] = mergedRef;
+    $[5] = t2;
+  } else {
+    t2 = $[5];
+  }
+  return t2;
+}
+
+```
+      

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/ref-initialization-call-2.expect.md

@@ -0,0 +1,46 @@
+
+## Input
+
+```javascript
+//@flow
+import {useRef} from 'react';
+
+/**
+ * Allowed: we aren't sure that the ref.current value flows into the render
+ * output, so we optimistically assume it's safe
+ */
+component C() {
+  const r = useRef(null);
+  if (r.current == null) {
+    f(r);
+  }
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: C,
+  params: [{}],
+};
+
+```
+
+## Code
+
+```javascript
+import { useRef } from "react";
+
+function C() {
+  const r = useRef(null);
+  if (r.current == null) {
+    f(r);
+  }
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: C,
+  params: [{}],
+};
+
+```
+      
+### Eval output
+(kind: exception) f is not defined

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/ref-initialization-call-2.js

@@ -1,6 +1,10 @@
 //@flow
 import {useRef} from 'react';
 
+/**
+ * Allowed: we aren't sure that the ref.current value flows into the render
+ * output, so we optimistically assume it's safe
+ */
 component C() {
   const r = useRef(null);
   if (r.current == null) {

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/ref-initialization-call.expect.md

@@ -0,0 +1,46 @@
+
+## Input
+
+```javascript
+//@flow
+import {useRef} from 'react';
+
+/**
+ * Allowed: we aren't sure that the ref.current value flows into the render
+ * output, so we optimistically assume it's safe
+ */
+component C() {
+  const r = useRef(null);
+  if (r.current == null) {
+    f(r.current);
+  }
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: C,
+  params: [{}],
+};
+
+```
+
+## Code
+
+```javascript
+import { useRef } from "react";
+
+function C() {
+  const r = useRef(null);
+  if (r.current == null) {
+    f(r.current);
+  }
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: C,
+  params: [{}],
+};
+
+```
+      
+### Eval output
+(kind: exception) f is not defined

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/ref-initialization-call.js

@@ -1,6 +1,10 @@
 //@flow
 import {useRef} from 'react';
 
+/**
+ * Allowed: we aren't sure that the ref.current value flows into the render
+ * output, so we optimistically assume it's safe
+ */
 component C() {
   const r = useRef(null);
   if (r.current == null) {

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/ref-initialization-post-access-2.expect.md

@@ -0,0 +1,49 @@
+
+## Input
+
+```javascript
+//@flow
+import {useRef} from 'react';
+
+/**
+ * Allowed: we aren't sure that the ref.current value flows into the render
+ * output, so we optimistically assume it's safe
+ */
+component C() {
+  const r = useRef(null);
+  if (r.current == null) {
+    r.current = 1;
+  }
+  f(r.current);
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: C,
+  params: [{}],
+};
+
+```
+
+## Code
+
+```javascript
+import { useRef } from "react";
+
+function C() {
+  const r = useRef(null);
+  if (r.current == null) {
+    r.current = 1;
+  }
+
+  f(r.current);
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: C,
+  params: [{}],
+};
+
+```
+      
+### Eval output
+(kind: exception) f is not defined

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/ref-initialization-post-access-2.js

@@ -1,6 +1,10 @@
 //@flow
 import {useRef} from 'react';
 
+/**
+ * Allowed: we aren't sure that the ref.current value flows into the render
+ * output, so we optimistically assume it's safe
+ */
 component C() {
   const r = useRef(null);
   if (r.current == null) {

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/ref-value-in-custom-component-event-handler-wrapper.expect.md

@@ -0,0 +1,121 @@
+
+## Input
+
+```javascript
+// @enableInferEventHandlers
+import {useRef} from 'react';
+
+// Simulates a custom component wrapper
+function CustomForm({onSubmit, children}: any) {
+  return <form onSubmit={onSubmit}>{children}</form>;
+}
+
+// Simulates react-hook-form's handleSubmit
+function handleSubmit<T>(callback: (data: T) => void) {
+  return (event: any) => {
+    event.preventDefault();
+    callback({} as T);
+  };
+}
+
+function Component() {
+  const ref = useRef<HTMLInputElement>(null);
+
+  const onSubmit = (data: any) => {
+    // Allowed: we aren't sure that the ref.current value flows into the render
+    // output, so we optimistically assume it's safe
+    if (ref.current !== null) {
+      console.log(ref.current.value);
+    }
+  };
+
+  return (
+    <>
+      <input ref={ref} />
+      <CustomForm onSubmit={handleSubmit(onSubmit)}>
+        <button type="submit">Submit</button>
+      </CustomForm>
+    </>
+  );
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Component,
+  params: [{}],
+};
+
+```
+
+## Code
+
+```javascript
+import { c as _c } from "react/compiler-runtime"; // @enableInferEventHandlers
+import { useRef } from "react";
+
+// Simulates a custom component wrapper
+function CustomForm(t0) {
+  const $ = _c(3);
+  const { onSubmit, children } = t0;
+  let t1;
+  if ($[0] !== children || $[1] !== onSubmit) {
+    t1 = <form onSubmit={onSubmit}>{children}</form>;
+    $[0] = children;
+    $[1] = onSubmit;
+    $[2] = t1;
+  } else {
+    t1 = $[2];
+  }
+  return t1;
+}
+
+// Simulates react-hook-form's handleSubmit
+function handleSubmit(callback) {
+  const $ = _c(2);
+  let t0;
+  if ($[0] !== callback) {
+    t0 = (event) => {
+      event.preventDefault();
+      callback({} as T);
+    };
+    $[0] = callback;
+    $[1] = t0;
+  } else {
+    t0 = $[1];
+  }
+  return t0;
+}
+
+function Component() {
+  const $ = _c(1);
+  const ref = useRef(null);
+  let t0;
+  if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
+    const onSubmit = (data) => {
+      if (ref.current !== null) {
+        console.log(ref.current.value);
+      }
+    };
+    t0 = (
+      <>
+        <input ref={ref} />
+        <CustomForm onSubmit={handleSubmit(onSubmit)}>
+          <button type="submit">Submit</button>
+        </CustomForm>
+      </>
+    );
+    $[0] = t0;
+  } else {
+    t0 = $[0];
+  }
+  return t0;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Component,
+  params: [{}],
+};
+
+```
+      
+### Eval output
+(kind: ok) <input><form><button type="submit">Submit</button></form>

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/ref-value-in-custom-component-event-handler-wrapper.tsx

@@ -18,8 +18,8 @@ function Component() {
   const ref = useRef<HTMLInputElement>(null);
 
   const onSubmit = (data: any) => {
-    // This should error: passing function with ref access to custom component
-    // event handler, even though it would be safe on a native <form>
+    // Allowed: we aren't sure that the ref.current value flows into the render
+    // output, so we optimistically assume it's safe
     if (ref.current !== null) {
       console.log(ref.current.value);
     }

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/ref-value-in-event-handler-wrapper.expect.md

@@ -0,0 +1,83 @@
+
+## Input
+
+```javascript
+// @enableInferEventHandlers
+import {useRef} from 'react';
+
+// Simulates a handler wrapper
+function handleClick(value: any) {
+  return () => {
+    console.log(value);
+  };
+}
+
+function Component() {
+  const ref = useRef(null);
+
+  // Allowed: we aren't sure that the ref.current value flows into the render
+  // output, so we optimistically assume it's safe
+  return (
+    <>
+      <input ref={ref} />
+      <button onClick={handleClick(ref.current)}>Click</button>
+    </>
+  );
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Component,
+  params: [{}],
+};
+
+```
+
+## Code
+
+```javascript
+import { c as _c } from "react/compiler-runtime"; // @enableInferEventHandlers
+import { useRef } from "react";
+
+// Simulates a handler wrapper
+function handleClick(value) {
+  const $ = _c(2);
+  let t0;
+  if ($[0] !== value) {
+    t0 = () => {
+      console.log(value);
+    };
+    $[0] = value;
+    $[1] = t0;
+  } else {
+    t0 = $[1];
+  }
+  return t0;
+}
+
+function Component() {
+  const $ = _c(1);
+  const ref = useRef(null);
+  let t0;
+  if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
+    t0 = (
+      <>
+        <input ref={ref} />
+        <button onClick={handleClick(ref.current)}>Click</button>
+      </>
+    );
+    $[0] = t0;
+  } else {
+    t0 = $[0];
+  }
+  return t0;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Component,
+  params: [{}],
+};
+
+```
+      
+### Eval output
+(kind: ok) <input><button>Click</button>

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/ref-value-in-event-handler-wrapper.tsx

@@ -11,8 +11,8 @@ function handleClick(value: any) {
 function Component() {
   const ref = useRef(null);
 
-  // This should still error: passing ref.current directly to a wrapper
-  // The ref value is accessed during render, not in the event handler
+  // Allowed: we aren't sure that the ref.current value flows into the render
+  // output, so we optimistically assume it's safe
   return (
     <>
       <input ref={ref} />

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/use-ref-added-to-dep-without-type-info.expect.md

@@ -0,0 +1,59 @@
+
+## Input
+
+```javascript
+// @validateRefAccessDuringRender
+
+/**
+ * Allowed: we don't have sufficient type information to be sure that
+ * this accesses a ref during render. Type info is lost when ref is
+ * stored in an object field.
+ */
+function Foo({a}) {
+  const ref = useRef();
+  const val = {ref};
+  const x = {a, val: val.ref.current};
+
+  return <VideoList videos={x} />;
+}
+
+```
+
+## Code
+
+```javascript
+import { c as _c } from "react/compiler-runtime"; // @validateRefAccessDuringRender
+
+/**
+ * Allowed: we don't have sufficient type information to be sure that
+ * this accesses a ref during render. Type info is lost when ref is
+ * stored in an object field.
+ */
+function Foo(t0) {
+  const $ = _c(3);
+  const { a } = t0;
+  const ref = useRef();
+  let t1;
+  if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
+    t1 = { ref };
+    $[0] = t1;
+  } else {
+    t1 = $[0];
+  }
+  const val = t1;
+  let t2;
+  if ($[1] !== a) {
+    const x = { a, val: val.ref.current };
+    t2 = <VideoList videos={x} />;
+    $[1] = a;
+    $[2] = t2;
+  } else {
+    t2 = $[2];
+  }
+  return t2;
+}
+
+```
+      
+### Eval output
+(kind: exception) Fixture not implemented

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/use-ref-added-to-dep-without-type-info.js

@@ -0,0 +1,14 @@
+// @validateRefAccessDuringRender
+
+/**
+ * Allowed: we don't have sufficient type information to be sure that
+ * this accesses a ref during render. Type info is lost when ref is
+ * stored in an object field.
+ */
+function Foo({a}) {
+  const ref = useRef();
+  const val = {ref};
+  const x = {a, val: val.ref.current};
+
+  return <VideoList videos={x} />;
+}

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/valid-uncertain-impure-functions-in-render-via-render-helper.expect.md

@@ -0,0 +1,51 @@
+
+## Input
+
+```javascript
+// @validateNoImpureFunctionsInRender
+
+import {identity, makeArray} from 'shared-runtime';
+
+function Component() {
+  const now = Date.now();
+  const renderItem = () => {
+    const array = makeArray(now);
+    // we don't have an alias signature for identity(), so we optimistically
+    // assume this doesn't propagate the impurity
+    const hasDate = identity(array);
+    return <Bar hasDate={hasDate} />;
+  };
+  return <Foo renderItem={renderItem} />;
+}
+
+```
+
+## Code
+
+```javascript
+import { c as _c } from "react/compiler-runtime"; // @validateNoImpureFunctionsInRender
+
+import { identity, makeArray } from "shared-runtime";
+
+function Component() {
+  const $ = _c(1);
+  let t0;
+  if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
+    const now = Date.now();
+    const renderItem = () => {
+      const array = makeArray(now);
+      const hasDate = identity(array);
+      return <Bar hasDate={hasDate} />;
+    };
+    t0 = <Foo renderItem={renderItem} />;
+    $[0] = t0;
+  } else {
+    t0 = $[0];
+  }
+  return t0;
+}
+
+```
+      
+### Eval output
+(kind: exception) Fixture not implemented

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/valid-uncertain-impure-functions-in-render-via-render-helper.js

@@ -6,6 +6,8 @@ function Component() {
   const now = Date.now();
   const renderItem = () => {
     const array = makeArray(now);
+    // we don't have an alias signature for identity(), so we optimistically
+    // assume this doesn't propagate the impurity
     const hasDate = identity(array);
     return <Bar hasDate={hasDate} />;
   };

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/validate-mutate-ref-arg-in-render.expect.md

@@ -0,0 +1,51 @@
+
+## Input
+
+```javascript
+// @validateRefAccessDuringRender:true
+
+function Foo(props, ref) {
+  // Allowed: the value is not guaranteed to flow into something that's rendered
+  console.log(ref.current);
+  return <div>{props.bar}</div>;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Foo,
+  params: [{bar: 'foo'}, {ref: {cuurrent: 1}}],
+  isComponent: true,
+};
+
+```
+
+## Code
+
+```javascript
+import { c as _c } from "react/compiler-runtime"; // @validateRefAccessDuringRender:true
+
+function Foo(props, ref) {
+  const $ = _c(2);
+
+  console.log(ref.current);
+  let t0;
+  if ($[0] !== props.bar) {
+    t0 = <div>{props.bar}</div>;
+    $[0] = props.bar;
+    $[1] = t0;
+  } else {
+    t0 = $[1];
+  }
+  return t0;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Foo,
+  params: [{ bar: "foo" }, { ref: { cuurrent: 1 } }],
+  isComponent: true,
+};
+
+```
+      
+### Eval output
+(kind: ok) <div>foo</div>
+logs: [undefined]

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/validate-mutate-ref-arg-in-render.js

@@ -1,5 +1,7 @@
 // @validateRefAccessDuringRender:true
+
 function Foo(props, ref) {
+  // Allowed: the value is not guaranteed to flow into something that's rendered
   console.log(ref.current);
   return <div>{props.bar}</div>;
 }

compiler/packages/snap/src/constants.ts

@@ -26,5 +26,3 @@ export const FIXTURES_PATH = path.join(
   'compiler',
 );
 export const SNAPSHOT_EXTENSION = '.expect.md';
-export const FILTER_FILENAME = 'testfilter.txt';
-export const FILTER_PATH = path.join(PROJECT_ROOT, FILTER_FILENAME);

compiler/packages/snap/src/fixture-utils.ts

@@ -8,7 +8,7 @@
 import fs from 'fs/promises';
 import * as glob from 'glob';
 import path from 'path';
-import {FILTER_PATH, FIXTURES_PATH, SNAPSHOT_EXTENSION} from './constants';
+import {FIXTURES_PATH, SNAPSHOT_EXTENSION} from './constants';
 
 const INPUT_EXTENSIONS = [
   '.js',
@@ -22,19 +22,9 @@ const INPUT_EXTENSIONS = [
 ];
 
 export type TestFilter = {
-  debug: boolean;
   paths: Array<string>;
 };
 
-async function exists(file: string): Promise<boolean> {
-  try {
-    await fs.access(file);
-    return true;
-  } catch {
-    return false;
-  }
-}
-
 function stripExtension(filename: string, extensions: Array<string>): string {
   for (const ext of extensions) {
     if (filename.endsWith(ext)) {
@@ -44,37 +34,6 @@ function stripExtension(filename: string, extensions: Array<string>): string {
   return filename;
 }
 
-export async function readTestFilter(): Promise<TestFilter | null> {
-  if (!(await exists(FILTER_PATH))) {
-    throw new Error(`testfilter file not found at \`${FILTER_PATH}\``);
-  }
-
-  const input = await fs.readFile(FILTER_PATH, 'utf8');
-  const lines = input.trim().split('\n');
-
-  let debug: boolean = false;
-  const line0 = lines[0];
-  if (line0 != null) {
-    // Try to parse pragmas
-    let consumedLine0 = false;
-    if (line0.indexOf('@only') !== -1) {
-      consumedLine0 = true;
-    }
-    if (line0.indexOf('@debug') !== -1) {
-      debug = true;
-      consumedLine0 = true;
-    }
-
-    if (consumedLine0) {
-      lines.shift();
-    }
-  }
-  return {
-    debug,
-    paths: lines.filter(line => !line.trimStart().startsWith('//')),
-  };
-}
-
 export function getBasename(fixture: TestFixture): string {
   return stripExtension(path.basename(fixture.inputPath), INPUT_EXTENSIONS);
 }

compiler/packages/snap/src/runner-watch.ts

@@ -8,8 +8,8 @@
 import watcher from '@parcel/watcher';
 import path from 'path';
 import ts from 'typescript';
-import {FILTER_FILENAME, FIXTURES_PATH, PROJECT_ROOT} from './constants';
-import {TestFilter, readTestFilter} from './fixture-utils';
+import {FIXTURES_PATH, PROJECT_ROOT} from './constants';
+import {TestFilter} from './fixture-utils';
 import {execSync} from 'child_process';
 
 export function watchSrc(
@@ -117,6 +117,10 @@ export type RunnerState = {
   lastUpdate: number;
   mode: RunnerMode;
   filter: TestFilter | null;
+  debug: boolean;
+  // Input mode for interactive pattern entry
+  inputMode: 'none' | 'pattern';
+  inputBuffer: string;
 };
 
 function subscribeFixtures(
@@ -142,26 +146,6 @@ function subscribeFixtures(
   });
 }
 
-function subscribeFilterFile(
-  state: RunnerState,
-  onChange: (state: RunnerState) => void,
-) {
-  watcher.subscribe(PROJECT_ROOT, async (err, events) => {
-    if (err) {
-      console.error(err);
-      process.exit(1);
-    } else if (
-      events.findIndex(event => event.path.includes(FILTER_FILENAME)) !== -1
-    ) {
-      if (state.mode.filter) {
-        state.filter = await readTestFilter();
-        state.mode.action = RunnerAction.Test;
-        onChange(state);
-      }
-    }
-  });
-}
-
 function subscribeTsc(
   state: RunnerState,
   onChange: (state: RunnerState) => void,
@@ -200,15 +184,67 @@ function subscribeKeyEvents(
   onChange: (state: RunnerState) => void,
 ) {
   process.stdin.on('keypress', async (str, key) => {
+    // Handle input mode (pattern entry)
+    if (state.inputMode !== 'none') {
+      if (key.name === 'return') {
+        // Enter pressed - process input
+        const pattern = state.inputBuffer.trim();
+        state.inputMode = 'none';
+        state.inputBuffer = '';
+        process.stdout.write('\n');
+
+        if (pattern !== '') {
+          // Set the pattern as filter
+          state.filter = {paths: [pattern]};
+          state.mode.filter = true;
+          state.mode.action = RunnerAction.Test;
+          onChange(state);
+        }
+        // If empty, just exit input mode without changes
+        return;
+      } else if (key.name === 'escape') {
+        // Cancel input mode
+        state.inputMode = 'none';
+        state.inputBuffer = '';
+        process.stdout.write(' (cancelled)\n');
+        return;
+      } else if (key.name === 'backspace') {
+        if (state.inputBuffer.length > 0) {
+          state.inputBuffer = state.inputBuffer.slice(0, -1);
+          // Erase character: backspace, space, backspace
+          process.stdout.write('\b \b');
+        }
+        return;
+      } else if (str && !key.ctrl && !key.meta) {
+        // Regular character - accumulate and echo
+        state.inputBuffer += str;
+        process.stdout.write(str);
+        return;
+      }
+      return; // Ignore other keys in input mode
+    }
+
+    // Normal mode keypress handling
     if (key.name === 'u') {
       // u => update fixtures
       state.mode.action = RunnerAction.Update;
     } else if (key.name === 'q') {
       process.exit(0);
-    } else if (key.name === 'f') {
-      state.mode.filter = !state.mode.filter;
-      state.filter = state.mode.filter ? await readTestFilter() : null;
+    } else if (key.name === 'a') {
+      // a => exit filter mode and run all tests
+      state.mode.filter = false;
+      state.filter = null;
       state.mode.action = RunnerAction.Test;
+    } else if (key.name === 'd') {
+      // d => toggle debug logging
+      state.debug = !state.debug;
+      state.mode.action = RunnerAction.Test;
+    } else if (key.name === 'p') {
+      // p => enter pattern input mode
+      state.inputMode = 'pattern';
+      state.inputBuffer = '';
+      process.stdout.write('Pattern: ');
+      return; // Don't trigger onChange yet
     } else {
       // any other key re-runs tests
       state.mode.action = RunnerAction.Test;
@@ -219,21 +255,33 @@ function subscribeKeyEvents(
 
 export async function makeWatchRunner(
   onChange: (state: RunnerState) => void,
-  filterMode: boolean,
+  debugMode: boolean,
+  initialPattern?: string,
 ): Promise<void> {
-  const state = {
+  // Determine initial filter state
+  let filter: TestFilter | null = null;
+  let filterEnabled = false;
+
+  if (initialPattern) {
+    filter = {paths: [initialPattern]};
+    filterEnabled = true;
+  }
+
+  const state: RunnerState = {
     compilerVersion: 0,
     isCompilerBuildValid: false,
     lastUpdate: -1,
     mode: {
       action: RunnerAction.Test,
-      filter: filterMode,
+      filter: filterEnabled,
     },
-    filter: filterMode ? await readTestFilter() : null,
+    filter,
+    debug: debugMode,
+    inputMode: 'none',
+    inputBuffer: '',
   };
 
   subscribeTsc(state, onChange);
   subscribeFixtures(state, onChange);
   subscribeKeyEvents(state, onChange);
-  subscribeFilterFile(state, onChange);
 }

compiler/packages/snap/src/runner.ts

@@ -12,8 +12,8 @@ import * as readline from 'readline';
 import ts from 'typescript';
 import yargs from 'yargs';
 import {hideBin} from 'yargs/helpers';
-import {FILTER_PATH, PROJECT_ROOT} from './constants';
-import {TestFilter, getFixtures, readTestFilter} from './fixture-utils';
+import {PROJECT_ROOT} from './constants';
+import {TestFilter, getFixtures} from './fixture-utils';
 import {TestResult, TestResults, report, update} from './reporter';
 import {
   RunnerAction,
@@ -33,9 +33,9 @@ type RunnerOptions = {
   sync: boolean;
   workerThreads: boolean;
   watch: boolean;
-  filter: boolean;
   update: boolean;
   pattern?: string;
+  debug: boolean;
 };
 
 const opts: RunnerOptions = yargs
@@ -59,18 +59,16 @@ const opts: RunnerOptions = yargs
   .alias('u', 'update')
   .describe('update', 'Update fixtures')
   .default('update', false)
-  .boolean('filter')
-  .describe(
-    'filter',
-    'Only run fixtures which match the contents of testfilter.txt',
-  )
-  .default('filter', false)
   .string('pattern')
   .alias('p', 'pattern')
   .describe(
     'pattern',
     'Optional glob pattern to filter fixtures (e.g., "error.*", "use-memo")',
   )
+  .boolean('debug')
+  .alias('d', 'debug')
+  .describe('debug', 'Enable debug logging to print HIR for each pass')
+  .default('debug', false)
   .help('help')
   .strict()
   .parseSync(hideBin(process.argv)) as RunnerOptions;
@@ -82,12 +80,15 @@ async function runFixtures(
   worker: Worker & typeof runnerWorker,
   filter: TestFilter | null,
   compilerVersion: number,
+  debug: boolean,
+  requireSingleFixture: boolean,
 ): Promise<TestResults> {
   // We could in theory be fancy about tracking the contents of the fixtures
   // directory via our file subscription, but it's simpler to just re-read
   // the directory each time.
   const fixtures = await getFixtures(filter);
   const isOnlyFixture = filter !== null && fixtures.size === 1;
+  const shouldLog = debug && (!requireSingleFixture || isOnlyFixture);
 
   let entries: Array<[string, TestResult]>;
   if (!opts.sync) {
@@ -96,12 +97,7 @@ async function runFixtures(
     for (const [fixtureName, fixture] of fixtures) {
       work.push(
         worker
-          .transformFixture(
-            fixture,
-            compilerVersion,
-            (filter?.debug ?? false) && isOnlyFixture,
-            true,
-          )
+          .transformFixture(fixture, compilerVersion, shouldLog, true)
           .then(result => [fixtureName, result]),
       );
     }
@@ -113,7 +109,7 @@ async function runFixtures(
       let output = await runnerWorker.transformFixture(
         fixture,
         compilerVersion,
-        (filter?.debug ?? false) && isOnlyFixture,
+        shouldLog,
         true,
       );
       entries.push([fixtureName, output]);
@@ -128,7 +124,7 @@ async function onChange(
   worker: Worker & typeof runnerWorker,
   state: RunnerState,
 ) {
-  const {compilerVersion, isCompilerBuildValid, mode, filter} = state;
+  const {compilerVersion, isCompilerBuildValid, mode, filter, debug} = state;
   if (isCompilerBuildValid) {
     const start = performance.now();
 
@@ -142,6 +138,8 @@ async function onChange(
       worker,
       mode.filter ? filter : null,
       compilerVersion,
+      debug,
+      true, // requireSingleFixture in watch mode
     );
     const end = performance.now();
     if (mode.action === RunnerAction.Update) {
@@ -159,11 +157,13 @@ async function onChange(
   console.log(
     '\n' +
       (mode.filter
-        ? `Current mode = FILTER, filter test fixtures by "${FILTER_PATH}".`
+        ? `Current mode = FILTER, pattern = "${filter?.paths[0] ?? ''}".`
         : 'Current mode = NORMAL, run all test fixtures.') +
       '\nWaiting for input or file changes...\n' +
       'u     - update all fixtures\n' +
-      `f     - toggle (turn ${mode.filter ? 'off' : 'on'}) filter mode\n` +
+      `d     - toggle (turn ${debug ? 'off' : 'on'}) debug logging\n` +
+      'p     - enter pattern to filter fixtures\n' +
+      (mode.filter ? 'a     - run all tests (exit filter mode)\n' : '') +
       'q     - quit\n' +
       '[any] - rerun tests\n',
   );
@@ -180,15 +180,16 @@ export async function main(opts: RunnerOptions): Promise<void> {
   worker.getStderr().pipe(process.stderr);
   worker.getStdout().pipe(process.stdout);
 
-  // If pattern is provided, force watch mode off and use pattern filter
-  const shouldWatch = opts.watch && opts.pattern == null;
-  if (opts.watch && opts.pattern != null) {
-    console.warn('NOTE: --watch is ignored when a --pattern is supplied');
-  }
+  // Check if watch mode should be enabled
+  const shouldWatch = opts.watch;
 
   if (shouldWatch) {
-    makeWatchRunner(state => onChange(worker, state), opts.filter);
-    if (opts.filter) {
+    makeWatchRunner(
+      state => onChange(worker, state),
+      opts.debug,
+      opts.pattern,
+    );
+    if (opts.pattern) {
       /**
        * Warm up wormers when in watch mode. Loading the Forget babel plugin
        * and all of its transitive dependencies takes 1-3s (per worker) on a M1.
@@ -236,14 +237,17 @@ export async function main(opts: RunnerOptions): Promise<void> {
               let testFilter: TestFilter | null = null;
               if (opts.pattern) {
                 testFilter = {
-                  debug: true,
                   paths: [opts.pattern],
                 };
-              } else if (opts.filter) {
-                testFilter = await readTestFilter();
               }
 
-              const results = await runFixtures(worker, testFilter, 0);
+              const results = await runFixtures(
+                worker,
+                testFilter,
+                0,
+                opts.debug,
+                false, // no requireSingleFixture in non-watch mode
+              );
               if (opts.update) {
                 update(results);
                 isSuccess = true;